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

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Message-ID: <YGzw/77+zCNri22Z@google.com>
Date:   Tue, 6 Apr 2021 23:38:39 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Keqian Zhu <zhukeqian1@...wei.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Ben Gardon <bgardon@...gle.com>
Subject: Re: [PATCH] KVM: MMU: protect TDP MMU pages only down to required
 level

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@google.com
[2] https://lkml.kernel.org/r/b5ab72f2-970f-64bd-891c-48f1c303548d@redhat.com

> Please feel free to add:
> 
> Reviewed-by: Keqian Zhu <zhukeqian1@...wei.com>
> 
> 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@...gle.com>
> > Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> > ---
> >  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);
> >  
> >  	/*
> >