On 30/03/2016 22:38, Yu Zhao wrote:
> 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;
> }
>
Looks good, thanks!
Paolo
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