In absence of shadow dirty mask, there is no need to set page dirty
if page has never been writable. This is a tiny optimization but
good to have for people who care much about dirty page tracking.
Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
---
arch/x86/kvm/mmu.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 70e95d0..1ff4dbb 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -557,8 +557,15 @@ static bool mmu_spte_update(u64 *sptep, u64 new_spte)
!is_writable_pte(new_spte))
ret = true;
- if (!shadow_accessed_mask)
+ if (!shadow_accessed_mask) {
+ /*
+ * We don't set page dirty when dropping non-writable spte.
+ * So do it now if the new spte is becoming non-writable.
+ */
+ if (ret)
+ kvm_set_pfn_dirty(spte_to_pfn(old_spte));
return ret;
+ }
/*
* Flush TLB when accessed/dirty bits are changed in the page tables,
@@ -605,7 +612,8 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
if (!shadow_accessed_mask || old_spte & shadow_accessed_mask)
kvm_set_pfn_accessed(pfn);
- if (!shadow_dirty_mask || (old_spte & shadow_dirty_mask))
+ if (old_spte & (shadow_dirty_mask ? shadow_dirty_mask :
+ PT_WRITABLE_MASK))
kvm_set_pfn_dirty(pfn);
return 1;
}
--
2.8.0.rc3.226.g39d4020
--
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