Re: [PATCH] KVM: MMU: protect TDP MMU pages only down to required level

From: Sean Christopherson
Date: Tue Apr 06 2021 - 19:40:41 EST


On Tue, Apr 06, 2021, Keqian Zhu wrote:
> Hi Paolo,
>
> I'm just going to fix this issue, and found that you have done this ;-)

Ha, and meanwhile I'm having a serious case of deja vu[1]. It even received a
variant of the magic "Queued, thanks"[2]. Doesn't appear in either of the 5.12
pull requests though, must have gotten lost along the way.

[1] https://lkml.kernel.org/r/20210213005015.1651772-3-seanjc@xxxxxxxxxx
[2] https://lkml.kernel.org/r/b5ab72f2-970f-64bd-891c-48f1c303548d@xxxxxxxxxx

> Please feel free to add:
>
> Reviewed-by: Keqian Zhu <zhukeqian1@xxxxxxxxxx>
>
> Thanks,
> Keqian
>
> On 2021/4/2 20:17, Paolo Bonzini wrote:
> > When using manual protection of dirty pages, it is not necessary
> > to protect nested page tables down to the 4K level; instead KVM
> > can protect only hugepages in order to split them lazily, and
> > delay write protection at 4K-granularity until KVM_CLEAR_DIRTY_LOG.
> > This was overlooked in the TDP MMU, so do it there as well.
> >
> > Fixes: a6a0b05da9f37 ("kvm: x86/mmu: Support dirty logging for the TDP MMU")
> > Cc: Ben Gardon <bgardon@xxxxxxxxxx>
> > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > ---
> > arch/x86/kvm/mmu/mmu.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index efb41f31e80a..0d92a269c5fa 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -5538,7 +5538,7 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm,
> > flush = slot_handle_level(kvm, memslot, slot_rmap_write_protect,
> > start_level, KVM_MAX_HUGEPAGE_LEVEL, false);
> > if (is_tdp_mmu_enabled(kvm))
> > - flush |= kvm_tdp_mmu_wrprot_slot(kvm, memslot, PG_LEVEL_4K);
> > + flush |= kvm_tdp_mmu_wrprot_slot(kvm, memslot, start_level);
> > write_unlock(&kvm->mmu_lock);
> >
> > /*
> >