Patch "arm64: KVM: Do not use pgd_index to index stage-2 pgd" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

arm64: KVM: Do not use pgd_index to index stage-2 pgd

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     arm64-kvm-do-not-use-pgd_index-to-index-stage-2-pgd.patch

and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Marc Zyngier <[email protected]>
Date: Tue, 10 Mar 2015 19:07:00 +0000
Subject: arm64: KVM: Do not use pgd_index to index stage-2 pgd

From: Marc Zyngier <[email protected]>

commit 04b8dc85bf4a64517e3cf20e409eeaa503b15cc1 upstream.

[Since we don't backport commit c647355 (KVM: arm: Add initial dirty page locking support) for linux-3.14.y, there is no stage2_wp_range in arch/arm/kvm/mmu.c. So ignore the change in stage2_wp_range introduced by this patch.]

The kernel's pgd_index macro is designed to index a normal, page sized array. KVM is a bit diffferent, as we can use concatenated pages to have a bigger address space (for example 40bit IPA with 4kB pages gives us an 8kB PGD.

In the above case, the use of pgd_index will always return an index inside the first 4kB, which makes a guest that has memory above 0x8000000000 rather unhappy, as it spins forever in a page fault, whist the host happilly corrupts the lower pgd.

The obvious fix is to get our own kvm_pgd_index that does the right thing(tm).

Tested on X-Gene with a hacked kvmtool that put memory at a stupidly high address.

---
 arch/arm/include/asm/kvm_mmu.h   |    3 ++-
 arch/arm/kvm/mmu.c               |    6 +++---
 arch/arm64/include/asm/kvm_mmu.h |    2 ++
 3 files changed, 7 insertions(+), 4 deletions(-)

@@ -117,13 +117,14 @@ static inline void kvm_set_s2pmd_writabl
 	(__boundary - 1 < (end) - 1)? __boundary: (end);		\
 })
 
+#define kvm_pgd_index(addr)                    pgd_index(addr)
+
 static inline bool kvm_page_empty(void *ptr)
 {
 	struct page *ptr_page = virt_to_page(ptr);
 	return page_count(ptr_page) == 1;
 }
 
-
 #define kvm_pte_table_empty(ptep) kvm_page_empty(ptep)
 #define kvm_pmd_table_empty(pmdp) kvm_page_empty(pmdp)
 #define kvm_pud_table_empty(pudp) (0)

@@ -194,7 +194,7 @@ static void unmap_range(struct kvm *kvm,
 	phys_addr_t addr = start, end = start + size;
 	phys_addr_t next;
 
-	pgd = pgdp + pgd_index(addr);
+	pgd = pgdp + kvm_pgd_index(addr);
 	do {
 		next = kvm_pgd_addr_end(addr, end);
 		if (!pgd_none(*pgd))

@@ -264,7 +264,7 @@ static void stage2_flush_memslot(struct
 	phys_addr_t next;
 	pgd_t *pgd;
 
-	pgd = kvm->arch.pgd + pgd_index(addr);
+	pgd = kvm->arch.pgd + kvm_pgd_index(addr);
 	do {
 		next = kvm_pgd_addr_end(addr, end);
 		stage2_flush_puds(kvm, pgd, addr, next);

@@ -649,7 +649,7 @@ static pmd_t *stage2_get_pmd(struct kvm
 	pud_t *pud;
 	pmd_t *pmd;
 
-	pgd = kvm->arch.pgd + pgd_index(addr);
+	pgd = kvm->arch.pgd + kvm_pgd_index(addr);
 	pud = pud_offset(pgd, addr);
 	if (pud_none(*pud)) {
 		if (!cache)

@@ -69,6 +69,8 @@
 #define PTRS_PER_S2_PGD (1 << (KVM_PHYS_SHIFT - PGDIR_SHIFT))
 #define S2_PGD_ORDER	get_order(PTRS_PER_S2_PGD * sizeof(pgd_t))
 
+#define kvm_pgd_index(addr)    (((addr) >> PGDIR_SHIFT) & (PTRS_PER_S2_PGD - 1))
+
 int create_hyp_mappings(void *from, void *to);
 int create_hyp_io_mappings(void *from, void *to, phys_addr_t);
 void free_boot_hyp_pgd(void);

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/arm64-kvm-fix-hcr-setting-for-32bit-guests.patch queue-3.14/arm64-kvm-do-not-use-pgd_index-to-index-stage-2-pgd.patch queue-3.14/arm64-kvm-fix-tlb-invalidation-by-ipa-vmid.patch queue-3.14/arm-arm64-kvm-keep-elrsr-aisr-in-sync-with-software-model.patch queue-3.14/arm-arm64-kvm-require-in-kernel-vgic-for-the-arch-timers.patch queue-3.14/arm-kvm-force-execution-of-hcptr-access-on-vm-exit.patch