Skip to contentSkip to conversation

KVM: Dirty ring interface

PATCH Superseded Peter Xu 2 participants 16 messages Jul 8, 2020 – Jul 23, 2020

Subsystems (6)
Documentation x86 KVM Kselftest +2 more subsystems

v11 of 15 Superseded Latest is v15 →

lore
Share & tools
lore

Peter Xu

author
#0 lore raw

v11 cover KVM: Dirty ring interface

KVM branch:
https://github.com/xzpeter/linux/tree/kvm-dirty-ring

QEMU branch for testing:
https://github.com/xzpeter/qemu/tree/kvm-dirty-ring

v11:
- rebased to kvm/queue (seems the newest)
- removed kvm_dirty_ring_waitqueue() tracepoint since not used
- set memslot->as_id in kvm_delete_memslot() [Sean]
- let __copy_to_user() always return -EFAULT [Sean]
- rename 'r' in alloc_apic_access_page into 'hva' [Sean]

v10:
- remove unused identity_map_pfn in init_rmode_identity_map [syzbot]
- add "static" to kvm_dirty_ring_full [syzbot]
- kvm_page_in_dirty_ring() use "#if" macros for KVM_DIRTY_LOG_PAGE_OFFSET to quiesce syzbot [syzbot]
- s/false/null/ in gfn_to_memslot_dirty_bitmap() [syzbot]

v9:
- patch 3: __x86_set_memory_region: squash another trivial change to return (0xdeadull << 48) always for slot removal [Sean]
- pick r-bs for Drew

For previous versions, please refer to:

V1: https://lore.kernel.org/kvm/[email protected]
V2: https://lore.kernel.org/kvm/[email protected]
V3: https://lore.kernel.org/kvm/[email protected]
V4: https://lore.kernel.org/kvm/[email protected]
V5: https://lore.kernel.org/kvm/[email protected]
V6: https://lore.kernel.org/kvm/[email protected]
V7: https://lore.kernel.org/kvm/[email protected]
V8: https://lore.kernel.org/kvm/[email protected]
V9: https://lore.kernel.org/kvm/[email protected]
V10: https://lore.kernel.org/kvm/[email protected]/

Overview
============

This is a continued work from Lei Cao <[email protected]> and Paolo Bonzini on the KVM dirty ring interface.

The new dirty ring interface is another way to collect dirty pages for the virtual machines. It is different from the existing dirty logging interface in a few ways, majorly:

- Data format: The dirty data was in a ring format rather than a bitmap format, so dirty bits to sync for dirty logging does not depend on the size of guest memory any more, but speed of dirtying. Also, the dirty ring is per-vcpu, while the dirty bitmap is per-vm.

- Data copy: The sync of dirty pages does not need data copy any more, but instead the ring is shared between the userspace and kernel by page sharings (mmap() on vcpu fd)

- Interface: Instead of using the old KVM_GET_DIRTY_LOG, KVM_CLEAR_DIRTY_LOG interfaces, the new ring uses the new KVM_RESET_DIRTY_RINGS ioctl when we want to reset the collected dirty pages to protected mode again (works like KVM_CLEAR_DIRTY_LOG, but ring based). To collecting dirty bits, we only need to read the ring data, no ioctl is needed.

Ring Layout
===========

KVM dirty ring is per-vcpu. Each ring is an array of kvm_dirty_gfn defined as:

struct kvm_dirty_gfn {
        __u32 flags;
        __u32 slot; /* as_id | slot_id */
        __u64 offset;
};

Each GFN is a state machine itself. The state is embeded in the flags field, as defined in the uapi header:

/*
* KVM dirty GFN flags, defined as:
*

 * |---------------+---------------+--------------|
 * | bit 1 (reset) | bit 0 (dirty) | Status       |
 * |---------------+---------------+--------------|
 * |             0 |             0 | Invalid GFN  |
 * |             0 |             1 | Dirty GFN    |
 * |             1 |             X | GFN to reset |
 * |---------------+---------------+--------------|
 *
 * Lifecycle of a dirty GFN goes like:
 *
 *      dirtied         collected        reset
 * 00 -----------> 01 -------------> 1X -------+
 *  ^                                          |
 *  |                                          |
 *  +------------------------------------------+

*
* The userspace program is only responsible for the 01->1X state
* conversion (to collect dirty bits). Also, it must not skip any
* dirty bits so that dirty bits are always collected in sequence. */

Testing
=======

This series provided both the implementation of the KVM dirty ring and the test case. Also I've implemented the QEMU counterpart that can run with the new KVM, link can be found at the top of the cover letter. However that's still a very initial version which is prone to change and future optimizations.

I did some measurement with the new method with 24G guest running some dirty workload, I don't see any speedup so far, even in some heavy dirty load it'll be slower (e.g., when 800MB/s random dirty rate, kvm dirty ring takes average of ~73s to complete migration while dirty logging only needs average of ~55s). However that's understandable because 24G guest means only 1M dirty bitmap, that's still a suitable case for dirty logging. Meanwhile heavier workload means worst case for dirty ring.

More tests are welcomed if there's bigger host/guest, especially on COLO-like workload.

Please review, thanks.

Peter Xu (13):
KVM: Cache as_id in kvm_memory_slot
KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR]
KVM: Pass in kvm pointer into mark_page_dirty_in_slot()
KVM: X86: Implement ring-based dirty memory tracking
KVM: Make dirty ring exclusive to dirty bitmap log
KVM: Don't allocate dirty bitmap if dirty ring is enabled
KVM: selftests: Always clear dirty bitmap after iteration
KVM: selftests: Sync uapi/linux/kvm.h to tools/
KVM: selftests: Use a single binary for dirty/clear log test
KVM: selftests: Introduce after_vcpu_run hook for dirty log test
KVM: selftests: Add dirty ring buffer test
KVM: selftests: Let dirty_log_test async for dirty ring test
KVM: selftests: Add "-c" parameter to dirty log test

 Documentation/virt/kvm/api.rst                | 123 +++++
 arch/x86/include/asm/kvm_host.h               |   6 +-
 arch/x86/include/uapi/asm/kvm.h               |   1 +
 arch/x86/kvm/Makefile                         |   3 +-
 arch/x86/kvm/mmu/mmu.c                        |  10 +-
 arch/x86/kvm/svm/avic.c                       |   9 +-
 arch/x86/kvm/vmx/vmx.c                        |  96 ++--
 arch/x86/kvm/x86.c                            |  46 +-
 include/linux/kvm_dirty_ring.h                | 103 ++++
 include/linux/kvm_host.h                      |  19 +
 include/trace/events/kvm.h                    |  63 +++
 include/uapi/linux/kvm.h                      |  53 ++
 tools/include/uapi/linux/kvm.h                |  53 ++
 tools/testing/selftests/kvm/Makefile          |   2 -
 .../selftests/kvm/clear_dirty_log_test.c      |   6 -
 tools/testing/selftests/kvm/dirty_log_test.c  | 505 ++++++++++++++++--
 .../testing/selftests/kvm/include/kvm_util.h  |   4 +
 tools/testing/selftests/kvm/lib/kvm_util.c    |  72 ++-
 .../selftests/kvm/lib/kvm_util_internal.h     |   4 +
 virt/kvm/dirty_ring.c                         | 197 +++++++
 virt/kvm/kvm_main.c                           | 168 +++++-
 21 files changed, 1408 insertions(+), 135 deletions(-)
 create mode 100644 include/linux/kvm_dirty_ring.h
 delete mode 100644 tools/testing/selftests/kvm/clear_dirty_log_test.c
 create mode 100644 virt/kvm/dirty_ring.c
Signature · 1 line
2.26.2
author
#1 lore raw

PATCH v11 1/13 KVM: Cache as_id in kvm_memory_slot

Cache the address space ID just like the slot ID. It will be used in order to fill in the dirty ring entries.

Suggested-by Paolo Bonzini <[email protected]>
Suggested-by Sean Christopherson <[email protected]>
Signed-off-by Peter Xu <[email protected]>
---
 include/linux/kvm_host.h | 1 +
 virt/kvm/kvm_main.c      | 6 ++++++
 2 files changed, 7 insertions(+)
include/linux/kvm_host.h +1 -0
index 9edc6fc71a89..346ee5905359 100644
@@ -346,6 +346,7 @@ struct kvm_memory_slot {
 	unsigned long userspace_addr;
 	u32 flags;
 	short id;
+	u16 as_id;
 };
 
 static inline unsigned long kvm_dirty_bitmap_bytes(struct kvm_memory_slot *memslot)
virt/kvm/kvm_main.c +6 -0
index a852af5c3214..62b7d537e179 100644
@@ -1191,6 +1191,11 @@ static int kvm_delete_memslot(struct kvm *kvm,
 
 	memset(&new, 0, sizeof(new));
 	new.id = old->id;
+	/*
+	 * This is only for debugging purpose; it should never be referenced
+	 * for a removed memslot.
+	 */
+	new.as_id = as_id;
 
 	r = kvm_set_memslot(kvm, mem, old, &new, as_id, KVM_MR_DELETE);
 	if (r)

@@ -1257,6 +1262,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	if (!mem->memory_size)
 		return kvm_delete_memslot(kvm, mem, &old, as_id);
 
+	new.as_id = as_id;
 	new.id = id;
 	new.base_gfn = mem->guest_phys_addr >> PAGE_SHIFT;
 	new.npages = mem->memory_size >> PAGE_SHIFT;
Signature · 1 line
2.26.2
author
#3 lore raw

PATCH v11 2/13 KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR]

In reply to Peter Xu

Originally, we have three code paths that can dirty a page without vcpu context for X86:

- init_rmode_identity_map
- init_rmode_tss
- kvmgt_rw_gpa

init_rmode_identity_map and init_rmode_tss will be setup on destination VM no matter what (and the guest cannot even see them), so it does not make sense to track them at all.

To do this, allow __x86_set_memory_region() to return the userspace address that just allocated to the caller. Then in both of the functions we directly write to the userspace address instead of calling kvm_write_*() APIs.

Another trivial change is that we don't need to explicitly clear the identity page table root in init_rmode_identity_map() because no matter what we'll write to the whole page with 4M huge page entries.

Suggested-by Paolo Bonzini <[email protected]>
Signed-off-by Peter Xu <[email protected]>
---
 arch/x86/include/asm/kvm_host.h |  3 +-
 arch/x86/kvm/svm/avic.c         |  9 ++--
 arch/x86/kvm/vmx/vmx.c          | 88 ++++++++++++++++-----------------
 arch/x86/kvm/x86.c              | 37 +++++++++++---
 4 files changed, 81 insertions(+), 56 deletions(-)
arch/x86/include/asm/kvm_host.h +2 -1
index 97cb005c7aa7..f26bc2bdacf4 100644
@@ -1647,7 +1647,8 @@ void __kvm_request_immediate_exit(struct kvm_vcpu *vcpu);
 
 int kvm_is_in_guest(void);
 
-int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size);
+void __user *__x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
+				     u32 size);
 bool kvm_vcpu_is_reset_bsp(struct kvm_vcpu *vcpu);
 bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu);
arch/x86/kvm/svm/avic.c +6 -3
index ac830cd50830..f9d665bbfd68 100644
@@ -235,7 +235,8 @@ static u64 *avic_get_physical_id_entry(struct kvm_vcpu *vcpu,
  */
 static int avic_update_access_page(struct kvm *kvm, bool activate)
 {
-	int ret = 0;
+	void __user *ret;
+	int r = 0;
 
 	mutex_lock(&kvm->slots_lock);
 	/*

@@ -251,13 +252,15 @@ static int avic_update_access_page(struct kvm *kvm, bool activate)
 				      APIC_ACCESS_PAGE_PRIVATE_MEMSLOT,
 				      APIC_DEFAULT_PHYS_BASE,
 				      activate ? PAGE_SIZE : 0);
-	if (ret)
+	if (IS_ERR(ret)) {
+		r = PTR_ERR(ret);
 		goto out;
+	}
 
 	kvm->arch.apic_access_page_done = activate;
 out:
 	mutex_unlock(&kvm->slots_lock);
-	return ret;
+	return r;
 }
 
 static int avic_init_backing_page(struct kvm_vcpu *vcpu)
arch/x86/kvm/vmx/vmx.c +42 -46

151 lines not on this page · raw message

arch/x86/kvm/x86.c +31 -6
index 09ee54f5e385..65be4977f608 100644
@@ -9959,7 +9959,32 @@ void kvm_arch_sync_events(struct kvm *kvm)
 	kvm_free_pit(kvm);
 }
 
-int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
+#define  ERR_PTR_USR(e)  ((void __user *)ERR_PTR(e))
+
+/**
+ * __x86_set_memory_region: Setup KVM internal memory slot
+ *
+ * @kvm: the kvm pointer to the VM.
+ * @id: the slot ID to setup.
+ * @gpa: the GPA to install the slot (unused when @size == 0).
+ * @size: the size of the slot. Set to zero to uninstall a slot.
+ *
+ * This function helps to setup a KVM internal memory slot.  Specify
+ * @size > 0 to install a new slot, while @size == 0 to uninstall a
+ * slot.  The return code can be one of the following:
+ *
+ *   HVA:           on success (uninstall will return a bogus HVA)
+ *   -errno:        on error
+ *
+ * The caller should always use IS_ERR() to check the return value
+ * before use.  Note, the KVM internal memory slots are guaranteed to
+ * remain valid and unchanged until the VM is destroyed, i.e., the
+ * GPA->HVA translation will not change.  However, the HVA is a user
+ * address, i.e. its accessibility is not guaranteed, and must be
+ * accessed via __copy_{to,from}_user().
+ */
+void __user * __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
+				      u32 size)
 {
 	int i, r;
 	unsigned long hva, uninitialized_var(old_npages);

@@ -9968,12 +9993,12 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
 
 	/* Called with kvm->slots_lock held.  */
 	if (WARN_ON(id >= KVM_MEM_SLOTS_NUM))
-		return -EINVAL;
+		return ERR_PTR_USR(-EINVAL);
 
 	slot = id_to_memslot(slots, id);
 	if (size) {
 		if (slot && slot->npages)
-			return -EEXIST;
+			return ERR_PTR_USR(-EEXIST);
 
 		/*
 		 * MAP_SHARED to prevent internal slot pages from being moved

@@ -9982,7 +10007,7 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
 		hva = vm_mmap(NULL, 0, size, PROT_READ | PROT_WRITE,
 			      MAP_SHARED | MAP_ANONYMOUS, 0);
 		if (IS_ERR((void *)hva))
-			return PTR_ERR((void *)hva);
+			return (void __user *)hva;
 	} else {
 		if (!slot || !slot->npages)
 			return 0;

@@ -10001,13 +10026,13 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
 		m.memory_size = size;
 		r = __kvm_set_memory_region(kvm, &m);
 		if (r < 0)
-			return r;
+			return ERR_PTR_USR(r);
 	}
 
 	if (!size)
 		vm_munmap(hva, old_npages * PAGE_SIZE);
 
-	return 0;
+	return (void __user *)hva;
 }
 EXPORT_SYMBOL_GPL(__x86_set_memory_region);
Signature · 1 line
2.26.2
Reviewed-by on v11 2/13
#4 lore raw

Re: [PATCH v11 02/13] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR]

Quoted 16 lines · Peter Xu

Originally, we have three code paths that can dirty a page without vcpu context for X86:

- init_rmode_identity_map
- init_rmode_tss
- kvmgt_rw_gpa

init_rmode_identity_map and init_rmode_tss will be setup on destination VM no matter what (and the guest cannot even see them), so it does not make sense to track them at all.

To do this, allow __x86_set_memory_region() to return the userspace address that just allocated to the caller. Then in both of the functions we directly write to the userspace address instead of calling kvm_write_*() APIs.

Quoted 7 lines

Another trivial change is that we don't need to explicitly clear the identity page table root in init_rmode_identity_map() because no matter what we'll write to the whole page with 4M huge page entries.

Suggested-by Paolo Bonzini <[email protected]>
Signed-off-by Peter Xu <[email protected]>

---

Reviewed-by Sean Christopherson <[email protected]>
author
#5 lore raw

PATCH v11 3/13 KVM: Pass in kvm pointer into mark_page_dirty_in_slot()

In reply to Peter Xu

The context will be needed to implement the kvm dirty ring.

Signed-off-by Peter Xu <[email protected]>
---
 virt/kvm/kvm_main.c | 33 +++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 14 deletions(-)
virt/kvm/kvm_main.c +19 -14
index 62b7d537e179..32ff377dd019 100644
@@ -143,7 +143,9 @@ static void hardware_disable_all(void);
 
 static void kvm_io_bus_destroy(struct kvm_io_bus *bus);
 
-static void mark_page_dirty_in_slot(struct kvm_memory_slot *memslot, gfn_t gfn);
+static void mark_page_dirty_in_slot(struct kvm *kvm,
+				    struct kvm_memory_slot *memslot,
+				    gfn_t gfn);
 
 __visible bool kvm_rebooting;
 EXPORT_SYMBOL_GPL(kvm_rebooting);

@@ -2134,7 +2136,8 @@ int kvm_vcpu_map(struct kvm_vcpu *vcpu, gfn_t gfn, struct kvm_host_map *map)
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_map);
 
-static void __kvm_unmap_gfn(struct kvm_memory_slot *memslot,
+static void __kvm_unmap_gfn(struct kvm *kvm,
+			struct kvm_memory_slot *memslot,
 			struct kvm_host_map *map,
 			struct gfn_to_pfn_cache *cache,
 			bool dirty, bool atomic)

@@ -2159,7 +2162,7 @@ static void __kvm_unmap_gfn(struct kvm_memory_slot *memslot,
 #endif
 
 	if (dirty)
-		mark_page_dirty_in_slot(memslot, map->gfn);
+		mark_page_dirty_in_slot(kvm, memslot, map->gfn);
 
 	if (cache)
 		cache->dirty |= dirty;

@@ -2173,7 +2176,7 @@ static void __kvm_unmap_gfn(struct kvm_memory_slot *memslot,
 int kvm_unmap_gfn(struct kvm_vcpu *vcpu, struct kvm_host_map *map, 
 		  struct gfn_to_pfn_cache *cache, bool dirty, bool atomic)
 {
-	__kvm_unmap_gfn(gfn_to_memslot(vcpu->kvm, map->gfn), map,
+	__kvm_unmap_gfn(vcpu->kvm, gfn_to_memslot(vcpu->kvm, map->gfn), map,
 			cache, dirty, atomic);
 	return 0;
 }

@@ -2181,8 +2184,8 @@ EXPORT_SYMBOL_GPL(kvm_unmap_gfn);
 
 void kvm_vcpu_unmap(struct kvm_vcpu *vcpu, struct kvm_host_map *map, bool dirty)
 {
-	__kvm_unmap_gfn(kvm_vcpu_gfn_to_memslot(vcpu, map->gfn), map, NULL,
-			dirty, false);
+	__kvm_unmap_gfn(vcpu->kvm, kvm_vcpu_gfn_to_memslot(vcpu, map->gfn),
+			map, NULL, dirty, false);
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_unmap);
 

@@ -2356,7 +2359,8 @@ int kvm_vcpu_read_guest_atomic(struct kvm_vcpu *vcpu, gpa_t gpa,
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_read_guest_atomic);
 
-static int __kvm_write_guest_page(struct kvm_memory_slot *memslot, gfn_t gfn,
+static int __kvm_write_guest_page(struct kvm *kvm,
+				  struct kvm_memory_slot *memslot, gfn_t gfn,
 			          const void *data, int offset, int len)
 {
 	int r;

@@ -2368,7 +2372,7 @@ static int __kvm_write_guest_page(struct kvm_memory_slot *memslot, gfn_t gfn,
 	r = __copy_to_user((void __user *)addr + offset, data, len);
 	if (r)
 		return -EFAULT;
-	mark_page_dirty_in_slot(memslot, gfn);
+	mark_page_dirty_in_slot(kvm, memslot, gfn);
 	return 0;
 }
 

@@ -2377,7 +2381,7 @@ int kvm_write_guest_page(struct kvm *kvm, gfn_t gfn,
 {
 	struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
 
-	return __kvm_write_guest_page(slot, gfn, data, offset, len);
+	return __kvm_write_guest_page(kvm, slot, gfn, data, offset, len);
 }
 EXPORT_SYMBOL_GPL(kvm_write_guest_page);
 

@@ -2386,7 +2390,7 @@ int kvm_vcpu_write_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn,
 {
 	struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
 
-	return __kvm_write_guest_page(slot, gfn, data, offset, len);
+	return __kvm_write_guest_page(vcpu->kvm, slot, gfn, data, offset, len);
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_write_guest_page);
 

@@ -2505,7 +2509,7 @@ int kvm_write_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
 	r = __copy_to_user((void __user *)ghc->hva + offset, data, len);
 	if (r)
 		return -EFAULT;
-	mark_page_dirty_in_slot(ghc->memslot, gpa >> PAGE_SHIFT);
+	mark_page_dirty_in_slot(kvm, ghc->memslot, gpa >> PAGE_SHIFT);
 
 	return 0;
 }

@@ -2581,7 +2585,8 @@ int kvm_clear_guest(struct kvm *kvm, gpa_t gpa, unsigned long len)
 }
 EXPORT_SYMBOL_GPL(kvm_clear_guest);
 
-static void mark_page_dirty_in_slot(struct kvm_memory_slot *memslot,
+static void mark_page_dirty_in_slot(struct kvm *kvm,
+				    struct kvm_memory_slot *memslot,
 				    gfn_t gfn)
 {
 	if (memslot && memslot->dirty_bitmap) {

@@ -2596,7 +2601,7 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
 	struct kvm_memory_slot *memslot;
 
 	memslot = gfn_to_memslot(kvm, gfn);
-	mark_page_dirty_in_slot(memslot, gfn);
+	mark_page_dirty_in_slot(kvm, memslot, gfn);
 }
 EXPORT_SYMBOL_GPL(mark_page_dirty);
 

@@ -2605,7 +2610,7 @@ void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn)
 	struct kvm_memory_slot *memslot;
 
 	memslot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
-	mark_page_dirty_in_slot(memslot, gfn);
+	mark_page_dirty_in_slot(vcpu->kvm, memslot, gfn);
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_mark_page_dirty);
Signature · 1 line
2.26.2
author
#6 lore raw

PATCH v11 4/13 KVM: X86: Implement ring-based dirty memory tracking

In reply to Peter Xu

This patch is heavily based on previous work from Lei Cao <[email protected]> and Paolo Bonzini <[email protected]>. [1]

KVM currently uses large bitmaps to track dirty memory. These bitmaps are copied to userspace when userspace queries KVM for its dirty page information. The use of bitmaps is mostly sufficient for live migration, as large parts of memory are be dirtied from one log-dirty pass to another. However, in a checkpointing system, the number of dirty pages is small and in fact it is often bounded---the VM is paused when it has dirtied a pre-defined number of pages. Traversing a large, sparsely populated bitmap to find set bits is time-consuming, as is copying the bitmap to user-space.

A similar issue will be there for live migration when the guest memory is huge while the page dirty procedure is trivial. In that case for each dirty sync we need to pull the whole dirty bitmap to userspace and analyse every bit even if it's mostly zeros.

The preferred data structure for above scenarios is a dense list of guest frame numbers (GFN). This patch series stores the dirty list in kernel memory that can be memory mapped into userspace to allow speedy harvesting.

This patch enables dirty ring for X86 only. However it should be easily extended to other archs as well.

[1] https://patchwork.kernel.org/patch/10471409/

Signed-off-by Lei Cao <[email protected]>
Signed-off-by Paolo Bonzini <[email protected]>
Signed-off-by Peter Xu <[email protected]>
---
 Documentation/virt/kvm/api.rst  | 116 +++++++++++++++++++
 arch/x86/include/asm/kvm_host.h |   3 +
 arch/x86/include/uapi/asm/kvm.h |   1 +
 arch/x86/kvm/Makefile           |   3 +-
 arch/x86/kvm/mmu/mmu.c          |   8 ++
 arch/x86/kvm/vmx/vmx.c          |   8 +-
 arch/x86/kvm/x86.c              |   9 ++
 include/linux/kvm_dirty_ring.h  | 103 +++++++++++++++++
 include/linux/kvm_host.h        |  13 +++
 include/trace/events/kvm.h      |  63 ++++++++++
 include/uapi/linux/kvm.h        |  53 +++++++++
 virt/kvm/dirty_ring.c           | 197 ++++++++++++++++++++++++++++++++
 virt/kvm/kvm_main.c             | 113 +++++++++++++++++-
 13 files changed, 687 insertions(+), 3 deletions(-)
 create mode 100644 include/linux/kvm_dirty_ring.h
 create mode 100644 virt/kvm/dirty_ring.c
Documentation/virt/kvm/api.rst +116 -0
index 1cfe79b932d6..c6b9f083d216 100644
@@ -249,6 +249,7 @@ Based on their initialization different VMs may have different capabilities.
 It is thus encouraged to use the vm ioctl to query for capabilities (available
 with KVM_CAP_CHECK_EXTENSION_VM on the vm fd)
 
+
 4.5 KVM_GET_VCPU_MMAP_SIZE
 --------------------------
 

@@ -262,6 +263,18 @@ The KVM_RUN ioctl (cf.) communicates with userspace via a shared
 memory region.  This ioctl returns the size of that region.  See the
 KVM_RUN documentation for details.
 
+Besides the size of the KVM_RUN communication region, other areas of
+the VCPU file descriptor can be mmap-ed, including:
+
+- if KVM_CAP_COALESCED_MMIO is available, a page at
+  KVM_COALESCED_MMIO_PAGE_OFFSET * PAGE_SIZE; for historical reasons,
+  this page is included in the result of KVM_GET_VCPU_MMAP_SIZE.
+  KVM_CAP_COALESCED_MMIO is not documented yet.
+
+- if KVM_CAP_DIRTY_LOG_RING is available, a number of pages at
+  KVM_DIRTY_LOG_PAGE_OFFSET * PAGE_SIZE.  For more information on
+  KVM_CAP_DIRTY_LOG_RING, see section 8.3.
+
 
 4.6 KVM_SET_MEMORY_REGION
 -------------------------

@@ -6151,3 +6164,106 @@ KVM can therefore start protected VMs.
 This capability governs the KVM_S390_PV_COMMAND ioctl and the
 KVM_MP_STATE_LOAD MP_STATE. KVM_SET_MP_STATE can fail for protected
 guests when the state change is invalid.
+
+8.24 KVM_CAP_DIRTY_LOG_RING
+
+Architectures: x86
+Parameters: args[0] - size of the dirty log ring
+
+KVM is capable of tracking dirty memory using ring buffers that are
+mmaped into userspace; there is one dirty ring per vcpu.
+
+One dirty ring is defined as below internally:
+
+struct kvm_dirty_ring {
+	u32 dirty_index;
+	u32 reset_index;
+	u32 size;
+	u32 soft_limit;
+	struct kvm_dirty_gfn *dirty_gfns;
+	int index;
+};
+
+Dirty GFNs (Guest Frame Numbers) are stored in the dirty_gfns array.
+For each of the dirty entry it's defined as:
+
+struct kvm_dirty_gfn {
+        __u32 flags;
+        __u32 slot; /* as_id | slot_id */
+        __u64 offset;
+};
+
+Each GFN is a state machine itself.  The state is embeded in the flags
+field, as defined in the uapi header:
+
+/*
+ * KVM dirty GFN flags, defined as:
+ *
+ * |---------------+---------------+--------------|
+ * | bit 1 (reset) | bit 0 (dirty) | Status       |
+ * |---------------+---------------+--------------|
+ * |             0 |             0 | Invalid GFN  |
+ * |             0 |             1 | Dirty GFN    |
+ * |             1 |             X | GFN to reset |
+ * |---------------+---------------+--------------|
+ *
+ * Lifecycle of a dirty GFN goes like:
+ *
+ *      dirtied         collected        reset
+ * 00 -----------> 01 -------------> 1X -------+
+ *  ^                                          |
+ *  |                                          |
+ *  +------------------------------------------+
+ *
+ * The userspace program is only responsible for the 01->1X state
+ * conversion (to collect dirty bits).  Also, it must not skip any
+ * dirty bits so that dirty bits are always collected in sequence.
+ */
+#define KVM_DIRTY_GFN_F_DIRTY           BIT(0)
+#define KVM_DIRTY_GFN_F_RESET           BIT(1)
+#define KVM_DIRTY_GFN_F_MASK            0x3
+
+Userspace calls KVM_ENABLE_CAP ioctl right after KVM_CREATE_VM ioctl
+to enable this capability for the new guest and set the size of the
+rings.  It is only allowed before creating any vCPU, and the size of
+the ring must be a power of two.  The larger the ring buffer, the less
+likely the ring is full and the VM is forced to exit to userspace. The
+optimal size depends on the workload, but it is recommended that it be
+at least 64 KiB (4096 entries).
+
+Just like for dirty page bitmaps, the buffer tracks writes to
+all user memory regions for which the KVM_MEM_LOG_DIRTY_PAGES flag was
+set in KVM_SET_USER_MEMORY_REGION.  Once a memory region is registered
+with the flag set, userspace can start harvesting dirty pages from the
+ring buffer.
+
+To harvest the dirty pages, userspace accesses the mmaped ring buffer
+to read the dirty GFNs starting from zero.  If the flags has the DIRTY
+bit set (at this stage the RESET bit must be cleared), then it means
+this GFN is a dirty GFN.  The userspace should collect this GFN and
+mark the flags from state 01b to 1Xb (bit 0 will be ignored by KVM,
+but bit 1 must be set to show that this GFN is collected and waiting
+for a reset), and move on to the next GFN.  The userspace should
+continue to do this until when the flags of a GFN has the DIRTY bit
+cleared, it means we've collected all the dirty GFNs we have for now.
+It's not a must that the userspace collects the all dirty GFNs in
+once.  However it must collect the dirty GFNs in sequence, i.e., the
+userspace program cannot skip one dirty GFN to collect the one next to
+it.
+
+After processing one or more entries in the ring buffer, userspace
+calls the VM ioctl KVM_RESET_DIRTY_RINGS to notify the kernel about
+it, so that the kernel will reprotect those collected GFNs.
+Therefore, the ioctl must be called *before* reading the content of
+the dirty pages.
+
+The dirty ring interface has a major difference comparing to the
+KVM_GET_DIRTY_LOG interface in that, when reading the dirty ring from
+userspace it's still possible that the kernel has not yet flushed the
+hardware dirty buffers into the kernel buffer (the flushing was
+previously done by the KVM_GET_DIRTY_LOG ioctl).  To achieve that, one
+needs to kick the vcpu out for a hardware buffer flush (vmexit) to
+make sure all the existing dirty gfns are flushed to the dirty rings.
+
+The dirty ring can gets full.  When it happens, the KVM_RUN of the
+vcpu will return with exit reason KVM_EXIT_DIRTY_LOG_FULL.
arch/x86/include/asm/kvm_host.h +3 -0
index f26bc2bdacf4..825ad3dc284a 100644
@@ -1188,6 +1188,7 @@ struct kvm_x86_ops {
 	void (*enable_log_dirty_pt_masked)(struct kvm *kvm,
 					   struct kvm_memory_slot *slot,
 					   gfn_t offset, unsigned long mask);
+	int (*cpu_dirty_log_size)(void);
 
 	/* pmu operations of sub-arch */
 	const struct kvm_pmu_ops *pmu_ops;

@@ -1695,4 +1696,6 @@ static inline int kvm_cpu_get_apicid(int mps_cpu)
 #define GET_SMSTATE(type, buf, offset)		\
 	(*(type *)((buf) + (offset) - 0x7e00))
 
+int kvm_cpu_dirty_log_size(void);
+
 #endif /* _ASM_X86_KVM_HOST_H */
arch/x86/include/uapi/asm/kvm.h +1 -0
index 17c5a038f42d..45fdaaf84c21 100644
@@ -12,6 +12,7 @@
 
 #define KVM_PIO_PAGE_OFFSET 1
 #define KVM_COALESCED_MMIO_PAGE_OFFSET 2
+#define KVM_DIRTY_LOG_PAGE_OFFSET 64
 
 #define DE_VECTOR 0
 #define DB_VECTOR 1
arch/x86/kvm/Makefile +2 -1
index 4a3081e9f4b5..b72c8db22c28 100644
@@ -10,7 +10,8 @@ endif
 KVM := ../../../virt/kvm
 
 kvm-y			+= $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o \
-				$(KVM)/eventfd.o $(KVM)/irqchip.o $(KVM)/vfio.o
+				$(KVM)/eventfd.o $(KVM)/irqchip.o $(KVM)/vfio.o \
+				$(KVM)/dirty_ring.o
 kvm-$(CONFIG_KVM_ASYNC_PF)	+= $(KVM)/async_pf.o
 
 kvm-y			+= x86.o emulate.o i8259.o irq.o lapic.o \
arch/x86/kvm/mmu/mmu.c +8 -0
index 69ddc3528362..1ed625445bef 100644
@@ -1739,6 +1739,14 @@ void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
 		kvm_mmu_write_protect_pt_masked(kvm, slot, gfn_offset, mask);
 }
 
+int kvm_cpu_dirty_log_size(void)
+{
+	if (kvm_x86_ops.cpu_dirty_log_size)
+		return kvm_x86_ops.cpu_dirty_log_size();
+
+	return 0;
+}
+
 bool kvm_mmu_slot_gfn_write_protect(struct kvm *kvm,
 				    struct kvm_memory_slot *slot, u64 gfn)
 {
arch/x86/kvm/vmx/vmx.c +7 -1
index 6e5208a735ec..18a60490dd34 100644
@@ -7827,6 +7827,11 @@ static bool vmx_check_apicv_inhibit_reasons(ulong bit)
 	return supported & BIT(bit);
 }
 
+static int vmx_cpu_dirty_log_size(void)
+{
+	return enable_pml ? PML_ENTITY_NUM : 0;
+}
+
 static struct kvm_x86_ops vmx_x86_ops __initdata = {
 	.hardware_unsetup = hardware_unsetup,
 

@@ -7954,6 +7959,7 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
 	.need_emulation_on_page_fault = vmx_need_emulation_on_page_fault,
 	.apic_init_signal_blocked = vmx_apic_init_signal_blocked,
 	.migrate_timers = vmx_migrate_timers,
+	.cpu_dirty_log_size = vmx_cpu_dirty_log_size,
 };
 
 static __init int hardware_setup(void)

@@ -8071,6 +8077,7 @@ static __init int hardware_setup(void)
 		vmx_x86_ops.slot_disable_log_dirty = NULL;
 		vmx_x86_ops.flush_log_dirty = NULL;
 		vmx_x86_ops.enable_log_dirty_pt_masked = NULL;
+		vmx_x86_ops.cpu_dirty_log_size = NULL;
 	}
 
 	if (!cpu_has_vmx_preemption_timer())

@@ -8134,7 +8141,6 @@ static struct kvm_x86_init_ops vmx_init_ops __initdata = {
 	.disabled_by_bios = vmx_disabled_by_bios,
 	.check_processor_compatibility = vmx_check_processor_compat,
 	.hardware_setup = hardware_setup,
-
 	.runtime_ops = &vmx_x86_ops,
 };
arch/x86/kvm/x86.c +9 -0
index 65be4977f608..280f587447d2 100644
@@ -8350,6 +8350,15 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 
 	bool req_immediate_exit = false;
 
+	/* Forbid vmenter if vcpu dirty ring is soft-full */
+	if (unlikely(vcpu->kvm->dirty_ring_size &&
+		     kvm_dirty_ring_soft_full(&vcpu->dirty_ring))) {
+		vcpu->run->exit_reason = KVM_EXIT_DIRTY_RING_FULL;
+		trace_kvm_dirty_ring_exit(vcpu);
+		r = 0;
+		goto out;
+	}
+
 	if (kvm_request_pending(vcpu)) {
 		if (kvm_check_request(KVM_REQ_GET_VMCS12_PAGES, vcpu)) {
 			if (unlikely(!kvm_x86_ops.nested_ops->get_vmcs12_pages(vcpu))) {
include/linux/kvm_dirty_ring.h new file +103 -0

103 lines not on this page · raw message

include/linux/kvm_host.h +13 -0
index 346ee5905359..824dd15df580 100644
@@ -34,6 +34,7 @@
 #include <linux/kvm_types.h>
 
 #include <asm/kvm_host.h>
+#include <linux/kvm_dirty_ring.h>
 
 #ifndef KVM_MAX_VCPU_ID
 #define KVM_MAX_VCPU_ID KVM_MAX_VCPUS

@@ -319,6 +320,7 @@ struct kvm_vcpu {
 	bool preempted;
 	bool ready;
 	struct kvm_vcpu_arch arch;
+	struct kvm_dirty_ring dirty_ring;
 };
 
 static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)

@@ -505,6 +507,7 @@ struct kvm {
 	struct srcu_struct irq_srcu;
 	pid_t userspace_pid;
 	unsigned int max_halt_poll_ns;
+	u32 dirty_ring_size;
 };
 
 #define kvm_err(fmt, ...) \

@@ -1440,4 +1443,14 @@ int kvm_vm_create_worker_thread(struct kvm *kvm, kvm_vm_thread_fn_t thread_fn,
 				uintptr_t data, const char *name,
 				struct task_struct **thread_ptr);
 
+/*
+ * This defines how many reserved entries we want to keep before we
+ * kick the vcpu to the userspace to avoid dirty ring full.  This
+ * value can be tuned to higher if e.g. PML is enabled on the host.
+ */
+#define  KVM_DIRTY_RING_RSVD_ENTRIES  64
+
+/* Max number of entries allowed for each kvm dirty ring */
+#define  KVM_DIRTY_RING_MAX_ENTRIES  65536
+
 #endif
include/trace/events/kvm.h +63 -0

69 lines not on this page · raw message

include/uapi/linux/kvm.h +53 -0

75 lines not on this page · raw message

virt/kvm/dirty_ring.c new file +197 -0

197 lines not on this page · raw message

virt/kvm/kvm_main.c +112 -1

186 lines not on this page · raw message

Signature · 1 line
2.26.2
author
#7 lore raw

PATCH v11 5/13 KVM: Make dirty ring exclusive to dirty bitmap log

In reply to Peter Xu

There's no good reason to use both the dirty bitmap logging and the new dirty ring buffer to track dirty bits. We should be able to even support both of them at the same time, but it could complicate things which could actually help little. Let's simply make it the rule before we enable dirty ring on any arch, that we don't allow these two interfaces to be used together.

The big world switch would be KVM_CAP_DIRTY_LOG_RING capability enablement. That's where we'll switch from the default dirty logging way to the dirty ring way. As long as kvm->dirty_ring_size is setup correctly, we'll once and for all switch to the dirty ring buffer mode for the current virtual machine.

Signed-off-by Peter Xu <[email protected]>
---
 Documentation/virt/kvm/api.rst |  7 +++++++
 virt/kvm/kvm_main.c            | 12 ++++++++++++
 2 files changed, 19 insertions(+)
Documentation/virt/kvm/api.rst +7 -0
index c6b9f083d216..ffade37a15ae 100644
@@ -6267,3 +6267,10 @@ make sure all the existing dirty gfns are flushed to the dirty rings.
 
 The dirty ring can gets full.  When it happens, the KVM_RUN of the
 vcpu will return with exit reason KVM_EXIT_DIRTY_LOG_FULL.
+
+NOTE: the capability KVM_CAP_DIRTY_LOG_RING and the corresponding
+ioctl KVM_RESET_DIRTY_RINGS are mutual exclusive to the existing ioctl
+KVM_GET_DIRTY_LOG.  After enabling KVM_CAP_DIRTY_LOG_RING with an
+acceptable dirty ring size, the virtual machine will switch to the
+dirty ring tracking mode.  Further ioctls to either KVM_GET_DIRTY_LOG
+or KVM_CLEAR_DIRTY_LOG will fail.
virt/kvm/kvm_main.c +12 -0
index 43e5536cfa93..c8c249edc885 100644
@@ -1374,6 +1374,10 @@ int kvm_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log,
 	unsigned long n;
 	unsigned long any = 0;
 
+	/* Dirty ring tracking is exclusive to dirty log tracking */
+	if (kvm->dirty_ring_size)
+		return -EINVAL;
+
 	*memslot = NULL;
 	*is_dirty = 0;
 

@@ -1435,6 +1439,10 @@ static int kvm_get_dirty_log_protect(struct kvm *kvm, struct kvm_dirty_log *log)
 	unsigned long *dirty_bitmap_buffer;
 	bool flush;
 
+	/* Dirty ring tracking is exclusive to dirty log tracking */
+	if (kvm->dirty_ring_size)
+		return -EINVAL;
+
 	as_id = log->slot >> 16;
 	id = (u16)log->slot;
 	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_USER_MEM_SLOTS)

@@ -1543,6 +1551,10 @@ static int kvm_clear_dirty_log_protect(struct kvm *kvm,
 	unsigned long *dirty_bitmap_buffer;
 	bool flush;
 
+	/* Dirty ring tracking is exclusive to dirty log tracking */
+	if (kvm->dirty_ring_size)
+		return -EINVAL;
+
 	as_id = log->slot >> 16;
 	id = (u16)log->slot;
 	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_USER_MEM_SLOTS)
Signature · 1 line
2.26.2
author
#8 lore raw

PATCH v11 6/13 KVM: Don't allocate dirty bitmap if dirty ring is enabled

In reply to Peter Xu

Because kvm dirty rings and kvm dirty log is used in an exclusive way, Let's avoid creating the dirty_bitmap when kvm dirty ring is enabled. At the meantime, since the dirty_bitmap will be conditionally created now, we can't use it as a sign of "whether this memory slot enabled dirty tracking". Change users like that to check against the kvm memory slot flags.

Note that there still can be chances where the kvm memory slot got its dirty_bitmap allocated, _if_ the memory slots are created before enabling of the dirty rings and at the same time with the dirty tracking capability enabled, they'll still with the dirty_bitmap. However it should not hurt much (e.g., the bitmaps will always be freed if they are there), and the real users normally won't trigger this because dirty bit tracking flag should in most cases only be applied to kvm slots only before migration starts, that should be far latter than kvm initializes (VM starts).

Signed-off-by Peter Xu <[email protected]>
---
 arch/x86/kvm/mmu/mmu.c   | 2 +-
 include/linux/kvm_host.h | 5 +++++
 virt/kvm/kvm_main.c      | 4 ++--
 3 files changed, 8 insertions(+), 3 deletions(-)
arch/x86/kvm/mmu/mmu.c +1 -1
index 1ed625445bef..df5ff9f0232a 100644
@@ -1278,7 +1278,7 @@ gfn_to_memslot_dirty_bitmap(struct kvm_vcpu *vcpu, gfn_t gfn,
 	slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
 	if (!slot || slot->flags & KVM_MEMSLOT_INVALID)
 		return NULL;
-	if (no_dirty_log && slot->dirty_bitmap)
+	if (no_dirty_log && kvm_slot_dirty_track_enabled(slot))
 		return NULL;
 
 	return slot;
include/linux/kvm_host.h +5 -0
index 824dd15df580..f749ac50c898 100644
@@ -351,6 +351,11 @@ struct kvm_memory_slot {
 	u16 as_id;
 };
 
+static inline bool kvm_slot_dirty_track_enabled(struct kvm_memory_slot *slot)
+{
+	return slot->flags & KVM_MEM_LOG_DIRTY_PAGES;
+}
+
 static inline unsigned long kvm_dirty_bitmap_bytes(struct kvm_memory_slot *memslot)
 {
 	return ALIGN(memslot->npages, BITS_PER_LONG) / 8;
virt/kvm/kvm_main.c +2 -2
index c8c249edc885..b5b6401c0270 100644
@@ -1313,7 +1313,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	/* Allocate/free page dirty bitmap as needed */
 	if (!(new.flags & KVM_MEM_LOG_DIRTY_PAGES))
 		new.dirty_bitmap = NULL;
-	else if (!new.dirty_bitmap) {
+	else if (!new.dirty_bitmap && !kvm->dirty_ring_size) {
 		r = kvm_alloc_dirty_bitmap(&new);
 		if (r)
 			return r;

@@ -2604,7 +2604,7 @@ static void mark_page_dirty_in_slot(struct kvm *kvm,
 				    struct kvm_memory_slot *memslot,
 				    gfn_t gfn)
 {
-	if (memslot && memslot->dirty_bitmap) {
+	if (memslot && kvm_slot_dirty_track_enabled(memslot)) {
 		unsigned long rel_gfn = gfn - memslot->base_gfn;
 		u32 slot = (memslot->as_id << 16) | memslot->id;
Signature · 1 line
2.26.2
author
#9 lore raw

PATCH v11 7/13 KVM: selftests: Always clear dirty bitmap after iteration

In reply to Peter Xu

We don't clear the dirty bitmap before because KVM_GET_DIRTY_LOG will clear it for us before copying the dirty log onto it. However we'd still better to clear it explicitly instead of assuming the kernel will always do it for us.

More importantly, in the upcoming dirty ring tests we'll start to fetch dirty pages from a ring buffer, so no one is going to clear the dirty bitmap for us.

Reviewed-by Andrew Jones <[email protected]>
Signed-off-by Peter Xu <[email protected]>
---
 tools/testing/selftests/kvm/dirty_log_test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
tools/testing/selftests/kvm/dirty_log_test.c +1 -1
index 752ec158ac59..6a8275a22861 100644
@@ -195,7 +195,7 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
 				    page);
 		}
 
-		if (test_bit_le(page, bmap)) {
+		if (test_and_clear_bit_le(page, bmap)) {
 			host_dirty_count++;
 			/*
 			 * If the bit is set, the value written onto
Signature · 1 line
2.26.2
author
#10 lore raw

PATCH v11 8/13 KVM: selftests: Sync uapi/linux/kvm.h to tools/

In reply to Peter Xu

This will be needed to extend the kvm selftest program.

Signed-off-by Peter Xu <[email protected]>
---
 tools/include/uapi/linux/kvm.h | 53 ++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
tools/include/uapi/linux/kvm.h +53 -0
index fdd632c833b4..4f7a0a7ce85a 100644
@@ -236,6 +236,7 @@ struct kvm_hyperv_exit {
 #define KVM_EXIT_IOAPIC_EOI       26
 #define KVM_EXIT_HYPERV           27
 #define KVM_EXIT_ARM_NISV         28
+#define KVM_EXIT_DIRTY_RING_FULL  29
 
 /* For KVM_EXIT_INTERNAL_ERROR */
 /* Emulate instruction failed. */

@@ -1017,6 +1018,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_S390_VCPU_RESETS 179
 #define KVM_CAP_S390_PROTECTED 180
 #define KVM_CAP_PPC_SECURE_GUEST 181
+#define KVM_CAP_DIRTY_LOG_RING 182
 
 #ifdef KVM_CAP_IRQ_ROUTING
 

@@ -1518,6 +1520,9 @@ struct kvm_pv_cmd {
 /* Available with KVM_CAP_S390_PROTECTED */
 #define KVM_S390_PV_COMMAND		_IOWR(KVMIO, 0xc5, struct kvm_pv_cmd)
 
+/* Available with KVM_CAP_DIRTY_LOG_RING */
+#define KVM_RESET_DIRTY_RINGS		_IO(KVMIO, 0xc6)
+
 /* Secure Encrypted Virtualization command */
 enum sev_cmd_id {
 	/* Guest initialization commands */

@@ -1671,4 +1676,52 @@ struct kvm_hyperv_eventfd {
 #define KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE    (1 << 0)
 #define KVM_DIRTY_LOG_INITIALLY_SET            (1 << 1)
 
+/*
+ * Arch needs to define the macro after implementing the dirty ring
+ * feature.  KVM_DIRTY_LOG_PAGE_OFFSET should be defined as the
+ * starting page offset of the dirty ring structures.
+ */
+#ifndef KVM_DIRTY_LOG_PAGE_OFFSET
+#define KVM_DIRTY_LOG_PAGE_OFFSET 0
+#endif
+
+/*
+ * KVM dirty GFN flags, defined as:
+ *
+ * |---------------+---------------+--------------|
+ * | bit 1 (reset) | bit 0 (dirty) | Status       |
+ * |---------------+---------------+--------------|
+ * |             0 |             0 | Invalid GFN  |
+ * |             0 |             1 | Dirty GFN    |
+ * |             1 |             X | GFN to reset |
+ * |---------------+---------------+--------------|
+ *
+ * Lifecycle of a dirty GFN goes like:
+ *
+ *      dirtied         collected        reset
+ * 00 -----------> 01 -------------> 1X -------+
+ *  ^                                          |
+ *  |                                          |
+ *  +------------------------------------------+
+ *
+ * The userspace program is only responsible for the 01->1X state
+ * conversion (to collect dirty bits).  Also, it must not skip any
+ * dirty bits so that dirty bits are always collected in sequence.
+ */
+#define KVM_DIRTY_GFN_F_DIRTY           BIT(0)
+#define KVM_DIRTY_GFN_F_RESET           BIT(1)
+#define KVM_DIRTY_GFN_F_MASK            0x3
+
+/*
+ * KVM dirty rings should be mapped at KVM_DIRTY_LOG_PAGE_OFFSET of
+ * per-vcpu mmaped regions as an array of struct kvm_dirty_gfn.  The
+ * size of the gfn buffer is decided by the first argument when
+ * enabling KVM_CAP_DIRTY_LOG_RING.
+ */
+struct kvm_dirty_gfn {
+	__u32 flags;
+	__u32 slot;
+	__u64 offset;
+};
+
 #endif /* __LINUX_KVM_H */
Signature · 1 line
2.26.2
author
#11 lore raw

PATCH v11 9/13 KVM: selftests: Use a single binary for dirty/clear log test

In reply to Peter Xu

Remove the clear_dirty_log test, instead merge it into the existing dirty_log_test. It should be cleaner to use this single binary to do both tests, also it's a preparation for the upcoming dirty ring test.

The default behavior will run all the modes in sequence.

Reviewed-by Andrew Jones <[email protected]>
Signed-off-by Peter Xu <[email protected]>
---
 tools/testing/selftests/kvm/Makefile          |   2 -
 .../selftests/kvm/clear_dirty_log_test.c      |   6 -
 tools/testing/selftests/kvm/dirty_log_test.c  | 187 +++++++++++++++---
 3 files changed, 156 insertions(+), 39 deletions(-)
 delete mode 100644 tools/testing/selftests/kvm/clear_dirty_log_test.c
tools/testing/selftests/kvm/Makefile +0 -2
index 4a166588d99f..6db4478e8921 100644
@@ -55,14 +55,12 @@ TEST_GEN_PROGS_x86_64 += x86_64/vmx_set_nested_state_test
 TEST_GEN_PROGS_x86_64 += x86_64/vmx_tsc_adjust_test
 TEST_GEN_PROGS_x86_64 += x86_64/xss_msr_test
 TEST_GEN_PROGS_x86_64 += x86_64/debug_regs
-TEST_GEN_PROGS_x86_64 += clear_dirty_log_test
 TEST_GEN_PROGS_x86_64 += demand_paging_test
 TEST_GEN_PROGS_x86_64 += dirty_log_test
 TEST_GEN_PROGS_x86_64 += kvm_create_max_vcpus
 TEST_GEN_PROGS_x86_64 += set_memory_region_test
 TEST_GEN_PROGS_x86_64 += steal_time
 
-TEST_GEN_PROGS_aarch64 += clear_dirty_log_test
 TEST_GEN_PROGS_aarch64 += demand_paging_test
 TEST_GEN_PROGS_aarch64 += dirty_log_test
 TEST_GEN_PROGS_aarch64 += kvm_create_max_vcpus
tools/testing/selftests/kvm/clear_dirty_log_test.c deleted +0 -6
deleted file mode 100644
index 11672ec6f74e..000000000000
@@ -1,6 +0,0 @@
-#define USE_CLEAR_DIRTY_LOG
-#define KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE (1 << 0)
-#define KVM_DIRTY_LOG_INITIALLY_SET         (1 << 1)
-#define KVM_DIRTY_LOG_MANUAL_CAPS   (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \
-		KVM_DIRTY_LOG_INITIALLY_SET)
-#include "dirty_log_test.c"
tools/testing/selftests/kvm/dirty_log_test.c +156 -31

259 lines not on this page · raw message

Signature · 1 line
2.26.2
author
#12 lore raw

PATCH v11 10/13 KVM: selftests: Introduce after_vcpu_run hook for dirty log test

In reply to Peter Xu

Provide a hook for the checks after vcpu_run() completes. Preparation for the dirty ring test because we'll need to take care of another exit reason.

Reviewed-by Andrew Jones <[email protected]>
Signed-off-by Peter Xu <[email protected]>
---
 tools/testing/selftests/kvm/dirty_log_test.c | 36 +++++++++++++-------
 1 file changed, 24 insertions(+), 12 deletions(-)
tools/testing/selftests/kvm/dirty_log_test.c +24 -12
index 139ccb550618..a2160946bcf5 100644
@@ -178,6 +178,15 @@ static void clear_log_collect_dirty_pages(struct kvm_vm *vm, int slot,
 	kvm_vm_clear_dirty_log(vm, slot, bitmap, 0, num_pages);
 }
 
+static void default_after_vcpu_run(struct kvm_vm *vm)
+{
+	struct kvm_run *run = vcpu_state(vm, VCPU_ID);
+
+	TEST_ASSERT(get_ucall(vm, VCPU_ID, NULL) == UCALL_SYNC,
+		    "Invalid guest sync status: exit_reason=%s\n",
+		    exit_reason_str(run->exit_reason));
+}
+
 struct log_mode {
 	const char *name;
 	/* Return true if this mode is supported, otherwise false */

@@ -187,16 +196,20 @@ struct log_mode {
 	/* Hook to collect the dirty pages into the bitmap provided */
 	void (*collect_dirty_pages) (struct kvm_vm *vm, int slot,
 				     void *bitmap, uint32_t num_pages);
+	/* Hook to call when after each vcpu run */
+	void (*after_vcpu_run)(struct kvm_vm *vm);
 } log_modes[LOG_MODE_NUM] = {
 	{
 		.name = "dirty-log",
 		.collect_dirty_pages = dirty_log_collect_dirty_pages,
+		.after_vcpu_run = default_after_vcpu_run,
 	},
 	{
 		.name = "clear-log",
 		.supported = clear_log_supported,
 		.create_vm_done = clear_log_create_vm_done,
 		.collect_dirty_pages = clear_log_collect_dirty_pages,
+		.after_vcpu_run = default_after_vcpu_run,
 	},
 };
 

@@ -247,6 +260,14 @@ static void log_mode_collect_dirty_pages(struct kvm_vm *vm, int slot,
 	mode->collect_dirty_pages(vm, slot, bitmap, num_pages);
 }
 
+static void log_mode_after_vcpu_run(struct kvm_vm *vm)
+{
+	struct log_mode *mode = &log_modes[host_log_mode];
+
+	if (mode->after_vcpu_run)
+		mode->after_vcpu_run(vm);
+}
+
 static void generate_random_array(uint64_t *guest_array, uint64_t size)
 {
 	uint64_t i;

@@ -261,25 +282,16 @@ static void *vcpu_worker(void *data)
 	struct kvm_vm *vm = data;
 	uint64_t *guest_array;
 	uint64_t pages_count = 0;
-	struct kvm_run *run;
-
-	run = vcpu_state(vm, VCPU_ID);
 
 	guest_array = addr_gva2hva(vm, (vm_vaddr_t)random_array);
-	generate_random_array(guest_array, TEST_PAGES_PER_LOOP);
 
 	while (!READ_ONCE(host_quit)) {
+		generate_random_array(guest_array, TEST_PAGES_PER_LOOP);
+		pages_count += TEST_PAGES_PER_LOOP;
 		/* Let the guest dirty the random pages */
 		ret = _vcpu_run(vm, VCPU_ID);
 		TEST_ASSERT(ret == 0, "vcpu_run failed: %d\n", ret);
-		if (get_ucall(vm, VCPU_ID, NULL) == UCALL_SYNC) {
-			pages_count += TEST_PAGES_PER_LOOP;
-			generate_random_array(guest_array, TEST_PAGES_PER_LOOP);
-		} else {
-			TEST_FAIL("Invalid guest sync status: "
-				  "exit_reason=%s\n",
-				  exit_reason_str(run->exit_reason));
-		}
+		log_mode_after_vcpu_run(vm);
 	}
 
 	pr_info("Dirtied %"PRIu64" pages\n", pages_count);
Signature · 1 line
2.26.2
author
#13 lore raw

PATCH v11 11/13 KVM: selftests: Add dirty ring buffer test

In reply to Peter Xu

Add the initial dirty ring buffer test.

The current test implements the userspace dirty ring collection, by only reaping the dirty ring when the ring is full.

So it's still running synchronously like this:

vcpu main thread

1. vcpu dirties pages
2. vcpu gets dirty ring full
(userspace exit)

3. main thread waits until full (so hardware buffers flushed)
4. main thread collects
5. main thread continues vcpu

6. vcpu continues, goes back to 1

We can't directly collects dirty bits during vcpu execution because otherwise we can't guarantee the hardware dirty bits were flushed when we collect and we're very strict on the dirty bits so otherwise we can fail the future verify procedure. A follow up patch will make this test to support async just like the existing dirty log test, by adding a vcpu kick mechanism.

Signed-off-by Peter Xu <[email protected]>
---
 tools/testing/selftests/kvm/dirty_log_test.c  | 201 +++++++++++++++++-
 .../testing/selftests/kvm/include/kvm_util.h  |   3 +
 tools/testing/selftests/kvm/lib/kvm_util.c    |  63 +++++-
 .../selftests/kvm/lib/kvm_util_internal.h     |   4 +
 4 files changed, 267 insertions(+), 4 deletions(-)
tools/testing/selftests/kvm/dirty_log_test.c +199 -2
index a2160946bcf5..531431cff4fc 100644
@@ -12,8 +12,10 @@
 #include <unistd.h>
 #include <time.h>
 #include <pthread.h>
+#include <semaphore.h>
 #include <linux/bitmap.h>
 #include <linux/bitops.h>
+#include <asm/barrier.h>
 
 #include "test_util.h"
 #include "kvm_util.h"

@@ -57,6 +59,8 @@
 # define test_and_clear_bit_le	test_and_clear_bit
 #endif
 
+#define TEST_DIRTY_RING_COUNT		1024
+
 /*
  * Guest/Host shared variables. Ensure addr_gva2hva() and/or
  * sync_global_to/from_guest() are used when accessing from

@@ -128,6 +132,10 @@ static uint64_t host_dirty_count;
 static uint64_t host_clear_count;
 static uint64_t host_track_next_count;
 
+/* Whether dirty ring reset is requested, or finished */
+static sem_t dirty_ring_vcpu_stop;
+static sem_t dirty_ring_vcpu_cont;
+
 enum log_mode_t {
 	/* Only use KVM_GET_DIRTY_LOG for logging */
 	LOG_MODE_DIRTY_LOG = 0,

@@ -135,6 +143,9 @@ enum log_mode_t {
 	/* Use both KVM_[GET|CLEAR]_DIRTY_LOG for logging */
 	LOG_MODE_CLEAR_LOG = 1,
 
+	/* Use dirty ring for logging */
+	LOG_MODE_DIRTY_RING = 2,
+
 	LOG_MODE_NUM,
 
 	/* Run all supported modes */

@@ -187,6 +198,120 @@ static void default_after_vcpu_run(struct kvm_vm *vm)
 		    exit_reason_str(run->exit_reason));
 }
 
+static bool dirty_ring_supported(void)
+{
+	return kvm_check_cap(KVM_CAP_DIRTY_LOG_RING);
+}
+
+static void dirty_ring_create_vm_done(struct kvm_vm *vm)
+{
+	/*
+	 * Switch to dirty ring mode after VM creation but before any
+	 * of the vcpu creation.
+	 */
+	vm_enable_dirty_ring(vm, TEST_DIRTY_RING_COUNT *
+			     sizeof(struct kvm_dirty_gfn));
+}
+
+static inline bool dirty_gfn_is_dirtied(struct kvm_dirty_gfn *gfn)
+{
+	return gfn->flags == KVM_DIRTY_GFN_F_DIRTY;
+}
+
+static inline void dirty_gfn_set_collected(struct kvm_dirty_gfn *gfn)
+{
+	gfn->flags = KVM_DIRTY_GFN_F_RESET;
+}
+
+static uint32_t dirty_ring_collect_one(struct kvm_dirty_gfn *dirty_gfns,
+				       int slot, void *bitmap,
+				       uint32_t num_pages, uint32_t *fetch_index)
+{
+	struct kvm_dirty_gfn *cur;
+	uint32_t count = 0;
+
+	while (true) {
+		cur = &dirty_gfns[*fetch_index % TEST_DIRTY_RING_COUNT];
+		if (!dirty_gfn_is_dirtied(cur))
+			break;
+		TEST_ASSERT(cur->slot == slot, "Slot number didn't match: "
+			    "%u != %u", cur->slot, slot);
+		TEST_ASSERT(cur->offset < num_pages, "Offset overflow: "
+			    "0x%llx >= 0x%x", cur->offset, num_pages);
+		pr_info("fetch 0x%x page %llu\n", *fetch_index, cur->offset);
+		set_bit(cur->offset, bitmap);
+		dirty_gfn_set_collected(cur);
+		(*fetch_index)++;
+		count++;
+	}
+
+	return count;
+}
+
+static void dirty_ring_collect_dirty_pages(struct kvm_vm *vm, int slot,
+					   void *bitmap, uint32_t num_pages)
+{
+	/* We only have one vcpu */
+	static uint32_t fetch_index = 0;
+	uint32_t count = 0, cleared;
+
+	/*
+	 * Before fetching the dirty pages, we need a vmexit of the
+	 * worker vcpu to make sure the hardware dirty buffers were
+	 * flushed.  This is not needed for dirty-log/clear-log tests
+	 * because get dirty log will natually do so.
+	 *
+	 * For now we do it in the simple way - we simply wait until
+	 * the vcpu uses up the soft dirty ring, then it'll always
+	 * do a vmexit to make sure that PML buffers will be flushed.
+	 * In real hypervisors, we probably need a vcpu kick or to
+	 * stop the vcpus (before the final sync) to make sure we'll
+	 * get all the existing dirty PFNs even cached in hardware.
+	 */
+	sem_wait(&dirty_ring_vcpu_stop);
+
+	/* Only have one vcpu */
+	count = dirty_ring_collect_one(vcpu_map_dirty_ring(vm, VCPU_ID),
+				       slot, bitmap, num_pages, &fetch_index);
+
+	cleared = kvm_vm_reset_dirty_ring(vm);
+
+	/* Cleared pages should be the same as collected */
+	TEST_ASSERT(cleared == count, "Reset dirty pages (%u) mismatch "
+		    "with collected (%u)", cleared, count);
+
+	pr_info("Notifying vcpu to continue\n");
+	sem_post(&dirty_ring_vcpu_cont);
+
+	pr_info("Iteration %ld collected %u pages\n", iteration, count);
+}
+
+static void dirty_ring_after_vcpu_run(struct kvm_vm *vm)
+{
+	struct kvm_run *run = vcpu_state(vm, VCPU_ID);
+
+	/* A ucall-sync or ring-full event is allowed */
+	if (get_ucall(vm, VCPU_ID, NULL) == UCALL_SYNC) {
+		/* We should allow this to continue */
+		;
+	} else if (run->exit_reason == KVM_EXIT_DIRTY_RING_FULL) {
+		sem_post(&dirty_ring_vcpu_stop);
+		pr_info("vcpu stops because dirty ring full...\n");
+		sem_wait(&dirty_ring_vcpu_cont);
+		pr_info("vcpu continues now.\n");
+	} else {
+		TEST_ASSERT(false, "Invalid guest sync status: "
+			    "exit_reason=%s\n",
+			    exit_reason_str(run->exit_reason));
+	}
+}
+
+static void dirty_ring_before_vcpu_join(void)
+{
+	/* Kick another round of vcpu just to make sure it will quit */
+	sem_post(&dirty_ring_vcpu_cont);
+}
+
 struct log_mode {
 	const char *name;
 	/* Return true if this mode is supported, otherwise false */

@@ -198,6 +323,7 @@ struct log_mode {
 				     void *bitmap, uint32_t num_pages);
 	/* Hook to call when after each vcpu run */
 	void (*after_vcpu_run)(struct kvm_vm *vm);
+	void (*before_vcpu_join) (void);
 } log_modes[LOG_MODE_NUM] = {
 	{
 		.name = "dirty-log",

@@ -211,6 +337,14 @@ struct log_mode {
 		.collect_dirty_pages = clear_log_collect_dirty_pages,
 		.after_vcpu_run = default_after_vcpu_run,
 	},
+	{
+		.name = "dirty-ring",
+		.supported = dirty_ring_supported,
+		.create_vm_done = dirty_ring_create_vm_done,
+		.collect_dirty_pages = dirty_ring_collect_dirty_pages,
+		.before_vcpu_join = dirty_ring_before_vcpu_join,
+		.after_vcpu_run = dirty_ring_after_vcpu_run,
+	},
 };
 
 /*

@@ -268,6 +402,14 @@ static void log_mode_after_vcpu_run(struct kvm_vm *vm)
 		mode->after_vcpu_run(vm);
 }
 
+static void log_mode_before_vcpu_join(void)
+{
+	struct log_mode *mode = &log_modes[host_log_mode];
+
+	if (mode->before_vcpu_join)
+		mode->before_vcpu_join();
+}
+
 static void generate_random_array(uint64_t *guest_array, uint64_t size)
 {
 	uint64_t i;

@@ -318,14 +460,65 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
 		}
 
 		if (test_and_clear_bit_le(page, bmap)) {
+			bool matched;
+
 			host_dirty_count++;
+
 			/*
 			 * If the bit is set, the value written onto
 			 * the corresponding page should be either the
 			 * previous iteration number or the current one.
 			 */
-			TEST_ASSERT(*value_ptr == iteration ||
-				    *value_ptr == iteration - 1,
+			matched = (*value_ptr == iteration ||
+				   *value_ptr == iteration - 1);
+
+			if (host_log_mode == LOG_MODE_DIRTY_RING && !matched) {
+				if (*value_ptr == iteration - 2) {
+					/*
+					 * Short answer: this case is special
+					 * only for dirty ring test where the
+					 * page is the last page before a kvm
+					 * dirty ring full in iteration N-2.
+					 *
+					 * Long answer: Assuming ring size R,
+					 * one possible condition is:
+					 *
+					 *      main thr       vcpu thr
+					 *      --------       --------
+					 *    iter=1
+					 *                   write 1 to page 0~(R-1)
+					 *                   full, vmexit
+					 *    collect 0~(R-1)
+					 *    kick vcpu
+					 *                   write 1 to (R-1)~(2R-2)
+					 *                   full, vmexit
+					 *    iter=2
+					 *    collect (R-1)~(2R-2)
+					 *    kick vcpu
+					 *                   write 1 to (2R-2)
+					 *                   (NOTE!!! "1" cached in cpu reg)
+					 *                   write 2 to (2R-1)~(3R-3)
+					 *                   full, vmexit
+					 *    iter=3
+					 *    collect (2R-2)~(3R-3)
+					 *    (here if we read value on page
+					 *     "2R-2" is 1, while iter=3!!!)
+					 */
+					matched = true;
+				} else {
+					/*
+					 * This is also special for dirty ring
+					 * when this page is exactly the last
+					 * page touched before vcpu ring full.
+					 * If it happens, we should expect the
+					 * value to change in the next round.
+					 */
+					set_bit_le(page, host_bmap_track);
+					continue;
+				}
+			}
+
+			TEST_ASSERT(matched,
 				    "Set page %"PRIu64" value %"PRIu64
 				    " incorrect (iteration=%"PRIu64")",
 				    page, *value_ptr, iteration);

@@ -488,6 +681,7 @@ static void run_test(enum vm_guest_mode mode, unsigned long iterations,
 
 	/* Tell the vcpu thread to quit */
 	host_quit = true;
+	log_mode_before_vcpu_join();
 	pthread_join(vcpu_thread, NULL);
 
 	pr_info("Total bits checked: dirty (%"PRIu64"), clear (%"PRIu64"), "

@@ -548,6 +742,9 @@ int main(int argc, char *argv[])
 	unsigned int mode;
 	int opt, i, j;
 
+	sem_init(&dirty_ring_vcpu_stop, 0, 0);
+	sem_init(&dirty_ring_vcpu_cont, 0, 0);
+
 #ifdef __x86_64__
 	guest_mode_init(VM_MODE_PXXV48_4K, true, true);
 #endif
tools/testing/selftests/kvm/include/kvm_util.h +3 -0
index 919e161dd289..dce07d354a70 100644
@@ -63,6 +63,7 @@ enum vm_mem_backing_src_type {
 
 int kvm_check_cap(long cap);
 int vm_enable_cap(struct kvm_vm *vm, struct kvm_enable_cap *cap);
+void vm_enable_dirty_ring(struct kvm_vm *vm, uint32_t ring_size);
 
 struct kvm_vm *vm_create(enum vm_guest_mode mode, uint64_t phy_pages, int perm);
 struct kvm_vm *_vm_create(enum vm_guest_mode mode, uint64_t phy_pages, int perm);

@@ -72,6 +73,7 @@ void kvm_vm_release(struct kvm_vm *vmp);
 void kvm_vm_get_dirty_log(struct kvm_vm *vm, int slot, void *log);
 void kvm_vm_clear_dirty_log(struct kvm_vm *vm, int slot, void *log,
 			    uint64_t first_page, uint32_t num_pages);
+uint32_t kvm_vm_reset_dirty_ring(struct kvm_vm *vm);
 
 int kvm_memcmp_hva_gva(void *hva, struct kvm_vm *vm, const vm_vaddr_t gva,
 		       size_t len);

@@ -196,6 +198,7 @@ void vcpu_nested_state_get(struct kvm_vm *vm, uint32_t vcpuid,
 int vcpu_nested_state_set(struct kvm_vm *vm, uint32_t vcpuid,
 			  struct kvm_nested_state *state, bool ignore_error);
 #endif
+void *vcpu_map_dirty_ring(struct kvm_vm *vm, uint32_t vcpuid);
 
 const char *exit_reason_str(unsigned int exit_reason);
tools/testing/selftests/kvm/lib/kvm_util.c +61 -2

102 lines not on this page · raw message

tools/testing/selftests/kvm/lib/kvm_util_internal.h +4 -0
index 2ef446520748..6a271c876e38 100644
@@ -28,6 +28,9 @@ struct vcpu {
 	uint32_t id;
 	int fd;
 	struct kvm_run *state;
+	struct kvm_dirty_gfn *dirty_gfns;
+	uint32_t fetch_index;
+	uint32_t dirty_gfns_count;
 };
 
 struct kvm_vm {

@@ -50,6 +53,7 @@ struct kvm_vm {
 	vm_paddr_t pgd;
 	vm_vaddr_t gdt;
 	vm_vaddr_t tss;
+	uint32_t dirty_ring_size;
 };
 
 struct vcpu *vcpu_find(struct kvm_vm *vm, uint32_t vcpuid);
Signature · 1 line
2.26.2
author
#14 lore raw

PATCH v11 12/13 KVM: selftests: Let dirty_log_test async for dirty ring test

In reply to Peter Xu

Previously the dirty ring test was working in synchronous way, because only with a vmexit (with that it was the ring full event) we'll know the hardware dirty bits will be flushed to the dirty ring.

With this patch we first introduced the vcpu kick mechanism by using SIGUSR1, meanwhile we can have a guarantee of vmexit and also the flushing of hardware dirty bits. With all these, we can keep the vcpu dirty work asynchronous of the whole collection procedure now. Still, we need to be very careful that we can only do it async if the vcpu is not reaching soft limit (no KVM_EXIT_DIRTY_RING_FULL). Otherwise we must collect the dirty bits before continuing the vcpu.

Further increase the dirty ring size to current maximum to make sure we torture more on the no-ring-full case, which should be the major scenario when the hypervisors like QEMU would like to use this feature.

Reviewed-by Andrew Jones <[email protected]>
Signed-off-by Peter Xu <[email protected]>
---
 tools/testing/selftests/kvm/dirty_log_test.c  | 126 +++++++++++++-----
 .../testing/selftests/kvm/include/kvm_util.h  |   1 +
 tools/testing/selftests/kvm/lib/kvm_util.c    |   9 ++
 3 files changed, 106 insertions(+), 30 deletions(-)
tools/testing/selftests/kvm/dirty_log_test.c +96 -30
index 531431cff4fc..4b404dfdc2f9 100644
@@ -13,6 +13,9 @@
 #include <time.h>
 #include <pthread.h>
 #include <semaphore.h>
+#include <sys/types.h>
+#include <signal.h>
+#include <errno.h>
 #include <linux/bitmap.h>
 #include <linux/bitops.h>
 #include <asm/barrier.h>

@@ -59,7 +62,9 @@
 # define test_and_clear_bit_le	test_and_clear_bit
 #endif
 
-#define TEST_DIRTY_RING_COUNT		1024
+#define TEST_DIRTY_RING_COUNT		65536
+
+#define SIG_IPI SIGUSR1
 
 /*
  * Guest/Host shared variables. Ensure addr_gva2hva() and/or

@@ -135,6 +140,12 @@ static uint64_t host_track_next_count;
 /* Whether dirty ring reset is requested, or finished */
 static sem_t dirty_ring_vcpu_stop;
 static sem_t dirty_ring_vcpu_cont;
+/*
+ * This is updated by the vcpu thread to tell the host whether it's a
+ * ring-full event.  It should only be read until a sem_wait() of
+ * dirty_ring_vcpu_stop and before vcpu continues to run.
+ */
+static bool dirty_ring_vcpu_ring_full;
 
 enum log_mode_t {
 	/* Only use KVM_GET_DIRTY_LOG for logging */

@@ -156,6 +167,33 @@ enum log_mode_t {
 static enum log_mode_t host_log_mode_option = LOG_MODE_ALL;
 /* Logging mode for current run */
 static enum log_mode_t host_log_mode;
+static pthread_t vcpu_thread;
+
+/* Only way to pass this to the signal handler */
+static struct kvm_vm *current_vm;
+
+static void vcpu_sig_handler(int sig)
+{
+	TEST_ASSERT(sig == SIG_IPI, "unknown signal: %d", sig);
+}
+
+static void vcpu_kick(void)
+{
+	pthread_kill(vcpu_thread, SIG_IPI);
+}
+
+/*
+ * In our test we do signal tricks, let's use a better version of
+ * sem_wait to avoid signal interrupts
+ */
+static void sem_wait_until(sem_t *sem)
+{
+	int ret;
+
+	do
+		ret = sem_wait(sem);
+	while (ret == -1 && errno == EINTR);
+}
 
 static bool clear_log_supported(void)
 {

@@ -189,10 +227,13 @@ static void clear_log_collect_dirty_pages(struct kvm_vm *vm, int slot,
 	kvm_vm_clear_dirty_log(vm, slot, bitmap, 0, num_pages);
 }
 
-static void default_after_vcpu_run(struct kvm_vm *vm)
+static void default_after_vcpu_run(struct kvm_vm *vm, int ret, int err)
 {
 	struct kvm_run *run = vcpu_state(vm, VCPU_ID);
 
+	TEST_ASSERT(ret == 0 || (ret == -1 && err == EINTR),
+		    "vcpu run failed: errno=%d", err);
+
 	TEST_ASSERT(get_ucall(vm, VCPU_ID, NULL) == UCALL_SYNC,
 		    "Invalid guest sync status: exit_reason=%s\n",
 		    exit_reason_str(run->exit_reason));

@@ -248,27 +289,37 @@ static uint32_t dirty_ring_collect_one(struct kvm_dirty_gfn *dirty_gfns,
 	return count;
 }
 
+static void dirty_ring_wait_vcpu(void)
+{
+	/* This makes sure that hardware PML cache flushed */
+	vcpu_kick();
+	sem_wait_until(&dirty_ring_vcpu_stop);
+}
+
+static void dirty_ring_continue_vcpu(void)
+{
+	pr_info("Notifying vcpu to continue\n");
+	sem_post(&dirty_ring_vcpu_cont);
+}
+
 static void dirty_ring_collect_dirty_pages(struct kvm_vm *vm, int slot,
 					   void *bitmap, uint32_t num_pages)
 {
 	/* We only have one vcpu */
 	static uint32_t fetch_index = 0;
 	uint32_t count = 0, cleared;
+	bool continued_vcpu = false;
 
-	/*
-	 * Before fetching the dirty pages, we need a vmexit of the
-	 * worker vcpu to make sure the hardware dirty buffers were
-	 * flushed.  This is not needed for dirty-log/clear-log tests
-	 * because get dirty log will natually do so.
-	 *
-	 * For now we do it in the simple way - we simply wait until
-	 * the vcpu uses up the soft dirty ring, then it'll always
-	 * do a vmexit to make sure that PML buffers will be flushed.
-	 * In real hypervisors, we probably need a vcpu kick or to
-	 * stop the vcpus (before the final sync) to make sure we'll
-	 * get all the existing dirty PFNs even cached in hardware.
-	 */
-	sem_wait(&dirty_ring_vcpu_stop);
+	dirty_ring_wait_vcpu();
+
+	if (!dirty_ring_vcpu_ring_full) {
+		/*
+		 * This is not a ring-full event, it's safe to allow
+		 * vcpu to continue
+		 */
+		dirty_ring_continue_vcpu();
+		continued_vcpu = true;
+	}
 
 	/* Only have one vcpu */
 	count = dirty_ring_collect_one(vcpu_map_dirty_ring(vm, VCPU_ID),

@@ -280,13 +331,16 @@ static void dirty_ring_collect_dirty_pages(struct kvm_vm *vm, int slot,
 	TEST_ASSERT(cleared == count, "Reset dirty pages (%u) mismatch "
 		    "with collected (%u)", cleared, count);
 
-	pr_info("Notifying vcpu to continue\n");
-	sem_post(&dirty_ring_vcpu_cont);
+	if (!continued_vcpu) {
+		TEST_ASSERT(dirty_ring_vcpu_ring_full,
+			    "Didn't continue vcpu even without ring full");
+		dirty_ring_continue_vcpu();
+	}
 
 	pr_info("Iteration %ld collected %u pages\n", iteration, count);
 }
 
-static void dirty_ring_after_vcpu_run(struct kvm_vm *vm)
+static void dirty_ring_after_vcpu_run(struct kvm_vm *vm, int ret, int err)
 {
 	struct kvm_run *run = vcpu_state(vm, VCPU_ID);
 

@@ -294,10 +348,16 @@ static void dirty_ring_after_vcpu_run(struct kvm_vm *vm)
 	if (get_ucall(vm, VCPU_ID, NULL) == UCALL_SYNC) {
 		/* We should allow this to continue */
 		;
-	} else if (run->exit_reason == KVM_EXIT_DIRTY_RING_FULL) {
+	} else if (run->exit_reason == KVM_EXIT_DIRTY_RING_FULL ||
+		   (ret == -1 && err == EINTR)) {
+		/* Update the flag first before pause */
+		WRITE_ONCE(dirty_ring_vcpu_ring_full,
+			   run->exit_reason == KVM_EXIT_DIRTY_RING_FULL);
 		sem_post(&dirty_ring_vcpu_stop);
-		pr_info("vcpu stops because dirty ring full...\n");
-		sem_wait(&dirty_ring_vcpu_cont);
+		pr_info("vcpu stops because %s...\n",
+			dirty_ring_vcpu_ring_full ?
+			"dirty ring is full" : "vcpu is kicked out");
+		sem_wait_until(&dirty_ring_vcpu_cont);
 		pr_info("vcpu continues now.\n");
 	} else {
 		TEST_ASSERT(false, "Invalid guest sync status: "

@@ -322,7 +382,7 @@ struct log_mode {
 	void (*collect_dirty_pages) (struct kvm_vm *vm, int slot,
 				     void *bitmap, uint32_t num_pages);
 	/* Hook to call when after each vcpu run */
-	void (*after_vcpu_run)(struct kvm_vm *vm);
+	void (*after_vcpu_run)(struct kvm_vm *vm, int ret, int err);
 	void (*before_vcpu_join) (void);
 } log_modes[LOG_MODE_NUM] = {
 	{

@@ -394,12 +454,12 @@ static void log_mode_collect_dirty_pages(struct kvm_vm *vm, int slot,
 	mode->collect_dirty_pages(vm, slot, bitmap, num_pages);
 }
 
-static void log_mode_after_vcpu_run(struct kvm_vm *vm)
+static void log_mode_after_vcpu_run(struct kvm_vm *vm, int ret, int err)
 {
 	struct log_mode *mode = &log_modes[host_log_mode];
 
 	if (mode->after_vcpu_run)
-		mode->after_vcpu_run(vm);
+		mode->after_vcpu_run(vm, ret, err);
 }
 
 static void log_mode_before_vcpu_join(void)

@@ -420,20 +480,27 @@ static void generate_random_array(uint64_t *guest_array, uint64_t size)
 
 static void *vcpu_worker(void *data)
 {
-	int ret;
+	int ret, vcpu_fd;
 	struct kvm_vm *vm = data;
 	uint64_t *guest_array;
 	uint64_t pages_count = 0;
+	struct sigaction sigact;
+
+	current_vm = vm;
+	vcpu_fd = vcpu_get_fd(vm, VCPU_ID);
+	memset(&sigact, 0, sizeof(sigact));
+	sigact.sa_handler = vcpu_sig_handler;
+	sigaction(SIG_IPI, &sigact, NULL);
 
 	guest_array = addr_gva2hva(vm, (vm_vaddr_t)random_array);
 
 	while (!READ_ONCE(host_quit)) {
+		/* Clear any existing kick signals */
 		generate_random_array(guest_array, TEST_PAGES_PER_LOOP);
 		pages_count += TEST_PAGES_PER_LOOP;
 		/* Let the guest dirty the random pages */
-		ret = _vcpu_run(vm, VCPU_ID);
-		TEST_ASSERT(ret == 0, "vcpu_run failed: %d\n", ret);
-		log_mode_after_vcpu_run(vm);
+		ret = ioctl(vcpu_fd, KVM_RUN, NULL);
+		log_mode_after_vcpu_run(vm, ret, errno);
 	}
 
 	pr_info("Dirtied %"PRIu64" pages\n", pages_count);

@@ -583,7 +650,6 @@ static struct kvm_vm *create_vm(enum vm_guest_mode mode, uint32_t vcpuid,
 static void run_test(enum vm_guest_mode mode, unsigned long iterations,
 		     unsigned long interval, uint64_t phys_offset)
 {
-	pthread_t vcpu_thread;
 	struct kvm_vm *vm;
 	unsigned long *bmap;
tools/testing/selftests/kvm/include/kvm_util.h +1 -0
index dce07d354a70..f3b5da383bb5 100644
@@ -146,6 +146,7 @@ vm_paddr_t addr_gva2gpa(struct kvm_vm *vm, vm_vaddr_t gva);
 struct kvm_run *vcpu_state(struct kvm_vm *vm, uint32_t vcpuid);
 void vcpu_run(struct kvm_vm *vm, uint32_t vcpuid);
 int _vcpu_run(struct kvm_vm *vm, uint32_t vcpuid);
+int vcpu_get_fd(struct kvm_vm *vm, uint32_t vcpuid);
 void vcpu_run_complete_io(struct kvm_vm *vm, uint32_t vcpuid);
 void vcpu_set_guest_debug(struct kvm_vm *vm, uint32_t vcpuid,
 			  struct kvm_guest_debug *debug);
tools/testing/selftests/kvm/lib/kvm_util.c +9 -0
index 831f986674ca..4625e193074e 100644
@@ -1220,6 +1220,15 @@ int _vcpu_run(struct kvm_vm *vm, uint32_t vcpuid)
 	return rc;
 }
 
+int vcpu_get_fd(struct kvm_vm *vm, uint32_t vcpuid)
+{
+	struct vcpu *vcpu = vcpu_find(vm, vcpuid);
+
+	TEST_ASSERT(vcpu != NULL, "vcpu not found, vcpuid: %u", vcpuid);
+
+	return vcpu->fd;
+}
+
 void vcpu_run_complete_io(struct kvm_vm *vm, uint32_t vcpuid)
 {
 	struct vcpu *vcpu = vcpu_find(vm, vcpuid);
Signature · 1 line
2.26.2
author
#15 lore raw

PATCH v11 13/13 KVM: selftests: Add "-c" parameter to dirty log test

In reply to Peter Xu

It's only used to override the existing dirty ring size/count. If with a bigger ring count, we test async of dirty ring. If with a smaller ring count, we test ring full code path. Async is default.

It has no use for non-dirty-ring tests.

Reviewed-by Andrew Jones <[email protected]>
Signed-off-by Peter Xu <[email protected]>
---
 tools/testing/selftests/kvm/dirty_log_test.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)
tools/testing/selftests/kvm/dirty_log_test.c +10 -3
index 4b404dfdc2f9..80c42c87265e 100644
@@ -168,6 +168,7 @@ static enum log_mode_t host_log_mode_option = LOG_MODE_ALL;
 /* Logging mode for current run */
 static enum log_mode_t host_log_mode;
 static pthread_t vcpu_thread;
+static uint32_t test_dirty_ring_count = TEST_DIRTY_RING_COUNT;
 
 /* Only way to pass this to the signal handler */
 static struct kvm_vm *current_vm;

@@ -250,7 +251,7 @@ static void dirty_ring_create_vm_done(struct kvm_vm *vm)
 	 * Switch to dirty ring mode after VM creation but before any
 	 * of the vcpu creation.
 	 */
-	vm_enable_dirty_ring(vm, TEST_DIRTY_RING_COUNT *
+	vm_enable_dirty_ring(vm, test_dirty_ring_count *
 			     sizeof(struct kvm_dirty_gfn));
 }
 

@@ -272,7 +273,7 @@ static uint32_t dirty_ring_collect_one(struct kvm_dirty_gfn *dirty_gfns,
 	uint32_t count = 0;
 
 	while (true) {
-		cur = &dirty_gfns[*fetch_index % TEST_DIRTY_RING_COUNT];
+		cur = &dirty_gfns[*fetch_index % test_dirty_ring_count];
 		if (!dirty_gfn_is_dirtied(cur))
 			break;
 		TEST_ASSERT(cur->slot == slot, "Slot number didn't match: "

@@ -778,6 +779,9 @@ static void help(char *name)
 	printf("usage: %s [-h] [-i iterations] [-I interval] "
 	       "[-p offset] [-m mode]\n", name);
 	puts("");
+	printf(" -c: specify dirty ring size, in number of entries\n");
+	printf("     (only useful for dirty-ring test; default: %"PRIu32")\n",
+	       TEST_DIRTY_RING_COUNT);
 	printf(" -i: specify iteration counts (default: %"PRIu64")\n",
 	       TEST_HOST_LOOP_N);
 	printf(" -I: specify interval in ms (default: %"PRIu64" ms)\n",

@@ -833,8 +837,11 @@ int main(int argc, char *argv[])
 	guest_mode_init(VM_MODE_P40V48_4K, true, true);
 #endif
 
-	while ((opt = getopt(argc, argv, "hi:I:p:m:M:")) != -1) {
+	while ((opt = getopt(argc, argv, "c:hi:I:p:m:M:")) != -1) {
 		switch (opt) {
+		case 'c':
+			test_dirty_ring_count = strtol(optarg, NULL, 10);
+			break;
 		case 'i':
 			iterations = strtol(optarg, NULL, 10);
 			break;
Signature · 1 line
2.26.2