Il 30/07/2013 15:02, Xiao Guangrong ha scritto:
> Make sure we can see the writable spte before the dirt bitmap is visible
>
> We do this is for kvm_vm_ioctl_get_dirty_log() write-protects the spte based
> on the dirty bitmap, we should ensure the writable spte can be found in rmap
> before the dirty bitmap is visible. Otherwise, we cleared the dirty bitmap and
> failed to write-protect the page
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/kvm/mmu.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 35d4b50..0fe56ad 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2486,12 +2486,12 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
> }
> }
>
> - if (pte_access & ACC_WRITE_MASK)
> - mark_page_dirty(vcpu->kvm, gfn);
> -
> set_pte:
> if (mmu_spte_update(sptep, spte))
> kvm_flush_remote_tlbs(vcpu->kvm);
> +
> + if (pte_access & ACC_WRITE_MASK)
> + mark_page_dirty(vcpu->kvm, gfn);
> done:
> return ret;
> }
>
What about this comment above:
/*
* Optimization: for pte sync, if spte was writable the hash
* lookup is unnecessary (and expensive). Write protection
* is responsibility of mmu_get_page / kvm_sync_page.
* Same reasoning can be applied to dirty page accounting.
*/
if (!can_unsync && is_writable_pte(*sptep))
goto set_pte;
if (mmu_need_write_protect(vcpu, gfn, can_unsync)) {
?
Should it be changed to
if (!can_unsync && is_writable_pte(*sptep))
pte_access &= ~ACC_WRITE_MASK; /* do not mark dirty */
else if (mmu_need_write_protect(vcpu, gfn, can_unsync)) {
?
Thanks,
Paolo
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