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kvm: set page dirty only if page has been writable

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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@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Yu Zhao 2016-03-30 13:38:09 -07:00 committed by Paolo Bonzini
parent 14ebda3394
commit 14f4760562
1 changed files with 10 additions and 2 deletions
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12
arch/x86/kvm/mmu.c
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@ -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;
}