[PATCH v2 4/4] KVM: MMU: Don't drop accessed bit while updating an spte

Avi Kivity
2010-06-07T07:11:01Z

__set_spte() will happily replace an spte with the accessed bit set with
one that has the accessed bit clear. Add a helper update_spte() which checks
for this condition and updates the page flag if needed.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
arch/x86/kvm/mmu.c | 25 +++++++++++++++++++++----
1 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index f5bb959..68e8923 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -305,6 +305,19 @@ static u64 __xchg_spte(u64 *sptep, u64 new_spte)
#endif
}

+static void update_spte(u64 *sptep, u64 new_spte)
+{
+ u64 old_spte;
+
+ if (!shadow_accessed_mask || (new_spte & shadow_accessed_mask)) {
+ __set_spte(sptep, new_spte);
+ } else {
+ old_spte = __xchg_spte(sptep, new_spte);
+ if (old_spte & shadow_accessed_mask)
+ mark_page_accessed(pfn_to_page(spte_to_pfn(old_spte)));
+ }
+}
+
static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache,
struct kmem_cache *base_cache, int min)
{
@@ -730,7 +743,7 @@ static int rmap_write_protect(struct kvm *kvm, u64 gfn)
BUG_ON(!(*spte & PT_PRESENT_MASK));
rmap_printk("rmap_write_protect: spte %p %llx\n", spte, *spte);
if (is_writable_pte(*spte)) {
- __set_spte(spte, *spte & ~PT_WRITABLE_MASK);
+ update_spte(spte, *spte & ~PT_WRITABLE_MASK);
write_protected = 1;
}
spte = rmap_next(kvm, rmapp, spte);
@@ -786,7 +799,7 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp,
unsigned long data)
{
int need_flush = 0;
- u64 *spte, new_spte;
+ u64 *spte, new_spte, old_spte;
pte_t *ptep = (pte_t *)data;
pfn_t new_pfn;

@@ -806,9 +819,13 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp,

new_spte &= ~PT_WRITABLE_MASK;
new_spte &= ~SPTE_HOST_WRITEABLE;
+ new_spte &= ~shadow_accessed_mask;
if (is_writable_pte(*spte))
kvm_set_pfn_dirty(spte_to_pfn(*spte));
- __set_spte(spte, new_spte);
+ old_spte = __xchg_spte(spte, new_spte);
+ if (is_shadow_present_pte(old_spte)
+ && (old_spte & shadow_accessed_mask))
+ mark_page_accessed(pfn_to_page(spte_to_pfn(old_spte)));
spte = rmap_next(kvm, rmapp, spte);
}
}
@@ -1956,7 +1973,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
mark_page_dirty(vcpu->kvm, gfn);

set_pte:
- __set_spte(sptep, spte);
+ update_spte(sptep, spte);
done:
return ret;
}
--
1.7.1