KVM: MMU: release noslot pfn on the fail path properly

PATCH In review Xiao Guangrong 1 participant 4 messages Sep 2, 2012

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x86 KVM KVM x86

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Xiao Guangrong

author

2012-09-02 12:56 UTC #0 lore raw

PATCH 1/6 KVM: MMU: release noslot pfn on the fail path properly

We can not directly call kvm_release_pfn_clean to release the pfn since we can meet noslot pfn which is used to cache mmio info into spte

Introduce mmu_release_pfn_clean to do this kind of thing

Signed-off-by Xiao Guangrong <[email protected]>

---
 arch/x86/kvm/mmu.c         |   19 ++++++++++++++-----
 arch/x86/kvm/paging_tmpl.h |    4 ++--
 2 files changed, 16 insertions(+), 7 deletions(-)

arch/x86/kvm/mmu.c +14 -5

index 399c177..3c10bca 100644
@@ -2432,6 +2432,16 @@ done:
 	return ret;
 }
 
+/*
+ * The primary user is page fault path which call it to properly
+ * release noslot_pfn.
+ */
+static void mmu_release_pfn_clean(pfn_t pfn)
+{
+	if (!is_error_pfn(pfn))
+		kvm_release_pfn_clean(pfn);
+}
+
 static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 			 unsigned pt_access, unsigned pte_access,
 			 int user_fault, int write_fault,

@@ -2497,8 +2507,7 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 		}
 	}
 
-	if (!is_error_pfn(pfn))
-		kvm_release_pfn_clean(pfn);
+	mmu_release_pfn_clean(pfn);
 }
 
 static void nonpaging_new_cr3(struct kvm_vcpu *vcpu)

@@ -2618,7 +2627,7 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
 					      1, ACC_ALL, iterator.sptep);
 			if (!sp) {
 				pgprintk("nonpaging_map: ENOMEM\n");
-				kvm_release_pfn_clean(pfn);
+				mmu_release_pfn_clean(pfn);
 				return -ENOMEM;
 			}

@@ -2882,7 +2891,7 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, u32 error_code,
 
 out_unlock:
 	spin_unlock(&vcpu->kvm->mmu_lock);
-	kvm_release_pfn_clean(pfn);
+	mmu_release_pfn_clean(pfn);
 	return 0;
 }

@@ -3350,7 +3359,7 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, u32 error_code,
 
 out_unlock:
 	spin_unlock(&vcpu->kvm->mmu_lock);
-	kvm_release_pfn_clean(pfn);
+	mmu_release_pfn_clean(pfn);
 	return 0;
 }

arch/x86/kvm/paging_tmpl.h +2 -2

index bf8c42b..f075259 100644
@@ -544,7 +544,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 out_gpte_changed:
 	if (sp)
 		kvm_mmu_put_page(sp, it.sptep);
-	kvm_release_pfn_clean(pfn);
+	mmu_release_pfn_clean(pfn);
 	return NULL;
 }

@@ -645,7 +645,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
 
 out_unlock:
 	spin_unlock(&vcpu->kvm->mmu_lock);
-	kvm_release_pfn_clean(pfn);
+	mmu_release_pfn_clean(pfn);
 	return 0;
 }

Signature · 1 line

1.7.7.6

Xiao Guangrong

author

2012-09-02 12:57 UTC #1 lore raw

PATCH 2/6 KVM: fix release error page

This bug was triggered:

[ 4220.198458] BUG: unable to handle kernel paging request at fffffffffffffffe
[ 4220.203907] IP: [<ffffffff81104d85>] put_page+0xf/0x34
......
[ 4220.237326] Call Trace:
[ 4220.237361]  [<ffffffffa03830d0>] kvm_arch_destroy_vm+0xf9/0x101 [kvm]
[ 4220.237382]  [<ffffffffa036fe53>] kvm_put_kvm+0xcc/0x127 [kvm]
[ 4220.237401]  [<ffffffffa03702bc>] kvm_vcpu_release+0x18/0x1c [kvm]
[ 4220.237407]  [<ffffffff81145425>] __fput+0x111/0x1ed
[ 4220.237411]  [<ffffffff8114550f>] ____fput+0xe/0x10
[ 4220.237418]  [<ffffffff81063511>] task_work_run+0x5d/0x88
[ 4220.237424]  [<ffffffff8104c3f7>] do_exit+0x2bf/0x7ca

The test case:

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <fcntl.h>
#include <unistd.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/mman.h>

#include <linux/kvm.h>

#define die(fmt, args...)	do {	\
	printf(fmt, ##args);		\
	exit(-1);} while (0)

static int create_vm(void)

{
	int sys_fd, vm_fd;

	sys_fd = open("/dev/kvm", O_RDWR);
	if (sys_fd < 0)
		die("open /dev/kvm fail.\n");

	vm_fd = ioctl(sys_fd, KVM_CREATE_VM, 0);
	if (vm_fd < 0)
		die("KVM_CREATE_VM fail.\n");

	return vm_fd;
}

static int create_vcpu(int vm_fd)

{
	int vcpu_fd;

	vcpu_fd = ioctl(vm_fd, KVM_CREATE_VCPU, 0);
	if (vcpu_fd < 0)
		die("KVM_CREATE_VCPU ioctl.\n");
	printf("Create vcpu.\n");
	return vcpu_fd;
}

static void *vcpu_thread(void *arg)

{
	int vm_fd = (int)(long)arg;

	create_vcpu(vm_fd);
	return NULL;
}

int main(int argc, char *argv[])

{
	pthread_t thread;
	int vm_fd;

	(void)argc;
	(void)argv;

	vm_fd = create_vm();
	pthread_create(&thread, NULL, vcpu_thread, (void *)(long)vm_fd);
	printf("Exit.\n");
	return 0;
}

It is caused by release kvm->arch.ept_identity_map_addr which is the error page.

The parent thread can send KILL signal to the vcpu thread when it was exiting which stops faulting pages and potentially allocating memory. So gfn_to_pfn/gfn_to_page may fail at this time

Fixed by checking the page before it is used

Signed-off-by Xiao Guangrong <[email protected]>

---
 arch/x86/kvm/vmx.c |   19 ++++++++++++++++---
 arch/x86/kvm/x86.c |   13 ++++++++++---
 2 files changed, 26 insertions(+), 6 deletions(-)

arch/x86/kvm/vmx.c +16 -3

index 248c2b4..ccea20a 100644
@@ -3590,6 +3590,7 @@ static void seg_setup(int seg)
 
 static int alloc_apic_access_page(struct kvm *kvm)
 {
+	struct page *page;
 	struct kvm_userspace_memory_region kvm_userspace_mem;
 	int r = 0;

@@ -3604,7 +3605,13 @@ static int alloc_apic_access_page(struct kvm *kvm)
 	if (r)
 		goto out;
 
-	kvm->arch.apic_access_page = gfn_to_page(kvm, 0xfee00);
+	page = gfn_to_page(kvm, 0xfee00);
+	if (is_error_page(page)) {
+		r = -EFAULT;
+		goto out;
+	}
+
+	kvm->arch.apic_access_page = page;
 out:
 	mutex_unlock(&kvm->slots_lock);
 	return r;

@@ -3612,6 +3619,7 @@ out:
 
 static int alloc_identity_pagetable(struct kvm *kvm)
 {
+	struct page *page;
 	struct kvm_userspace_memory_region kvm_userspace_mem;
 	int r = 0;

@@ -3627,8 +3635,13 @@ static int alloc_identity_pagetable(struct kvm *kvm)
 	if (r)
 		goto out;
 
-	kvm->arch.ept_identity_pagetable = gfn_to_page(kvm,
-			kvm->arch.ept_identity_map_addr >> PAGE_SHIFT);
+	page = gfn_to_page(kvm, kvm->arch.ept_identity_map_addr >> PAGE_SHIFT);
+	if (is_error_page(page)) {
+		r = -EFAULT;
+		goto out;
+	}
+
+	kvm->arch.ept_identity_pagetable = page;
 out:
 	mutex_unlock(&kvm->slots_lock);
 	return r;

arch/x86/kvm/x86.c +10 -3

index d8fba22..d44edaa 100644
@@ -5101,17 +5101,20 @@ static void post_kvm_run_save(struct kvm_vcpu *vcpu)
 			!kvm_event_needs_reinjection(vcpu);
 }
 
-static void vapic_enter(struct kvm_vcpu *vcpu)
+static int vapic_enter(struct kvm_vcpu *vcpu)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
 	struct page *page;
 
 	if (!apic || !apic->vapic_addr)
-		return;
+		return 0;
 
 	page = gfn_to_page(vcpu->kvm, apic->vapic_addr >> PAGE_SHIFT);
+	if (is_error_page(page))
+		return -EFAULT;
 
 	vcpu->arch.apic->vapic_page = page;
+	return 0;
 }
 
 static void vapic_exit(struct kvm_vcpu *vcpu)

@@ -5418,7 +5421,11 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 	}
 
 	vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
-	vapic_enter(vcpu);
+	r = vapic_enter(vcpu);
+	if (r) {
+		srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
+		return r;
+	}
 
 	r = 1;
 	while (r > 0) {

Signature · 1 line

1.7.7.6

Xiao Guangrong

author

2012-09-02 12:57 UTC #2 lore raw

PATCH 3/6 KVM: MMU: remove unnecessary check

In reply to Xiao Guangrong

Checking the return of kvm_mmu_get_page is unnecessary since it is guaranteed by memory cache

Signed-off-by Xiao Guangrong <[email protected]>

---
 arch/x86/kvm/mmu.c |    5 -----
 1 files changed, 0 insertions(+), 5 deletions(-)

arch/x86/kvm/mmu.c +0 -5

index 3c10bca..98cf4bf 100644
@@ -2625,11 +2625,6 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
 			sp = kvm_mmu_get_page(vcpu, pseudo_gfn, iterator.addr,
 					      iterator.level - 1,
 					      1, ACC_ALL, iterator.sptep);
-			if (!sp) {
-				pgprintk("nonpaging_map: ENOMEM\n");
-				mmu_release_pfn_clean(pfn);
-				return -ENOMEM;
-			}
 
 			mmu_spte_set(iterator.sptep,
 				     __pa(sp->spt)

Signature · 1 line

1.7.7.6

Xiao Guangrong

author

2012-09-02 13:51 UTC #3 lore raw

In reply to Xiao Guangrong

Sorry, i forgot to modify the patch title, total patch number is 3, so the title should be 1/3, 2/3, 3/3. :(

Quoted 7 lines · Xiao Guangrong

We can not directly call kvm_release_pfn_clean to release the pfn since we can meet noslot pfn which is used to cache mmio info into spte
Introduce mmu_release_pfn_clean to do this kind of thing
Signed-off-by Xiao Guangrong <[email protected]>