Re: [PATCH 1/2] KVM: x86/mmu: Skip tlb flush if it has been done in zap_gfn_range()

[Sean Christopherson]

On Wed, Nov 17, 2021, Paolo Bonzini wrote:
> On 11/17/21 10:20, Hou Wenlong wrote:
> > If the parameter flush is set, zap_gfn_range() would flush remote tlb
> > when yield, then tlb flush is not needed outside. So use the return
> > value of zap_gfn_range() directly instead of OR on it in
> > kvm_unmap_gfn_range() and kvm_tdp_mmu_unmap_gfn_range().
> > 
> > Fixes: 3039bcc744980 ("KVM: Move x86's MMU notifier memslot walkers to generic code")
> > Signed-off-by: Hou Wenlong <houwenlong93@xxxxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/kvm/mmu/mmu.c     | 2 +-
> >   arch/x86/kvm/mmu/tdp_mmu.c | 4 ++--
> >   2 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 354d2ca92df4..d57319e596a9 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -1582,7 +1582,7 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> >   		flush = kvm_handle_gfn_range(kvm, range, kvm_unmap_rmapp);
> >   	if (is_tdp_mmu_enabled(kvm))
> > -		flush |= kvm_tdp_mmu_unmap_gfn_range(kvm, range, flush);
> > +		flush = kvm_tdp_mmu_unmap_gfn_range(kvm, range, flush);
> >   	return flush;
> >   }
> > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> > index 7c5dd83e52de..9d03f5b127dc 100644
> > --- a/arch/x86/kvm/mmu/tdp_mmu.c
> > +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> > @@ -1034,8 +1034,8 @@ bool kvm_tdp_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range,
> >   	struct kvm_mmu_page *root;
> >   	for_each_tdp_mmu_root(kvm, root, range->slot->as_id)
> > -		flush |= zap_gfn_range(kvm, root, range->start, range->end,
> > -				       range->may_block, flush, false);
> > +		flush = zap_gfn_range(kvm, root, range->start, range->end,
> > +				      range->may_block, flush, false);
> >   	return flush;
> >   }
> > 
> 
> Queued both, thanks.

Please replace patch 02 with the below.  Hou's patch isn't wrong, but it's nowhere
near agressive enough in purging the unecessary flush.  I was too slow in writing
a changelog for this patch in my local repo.