Subject: Re: [PATCH v12 54/84] KVM: arm64: Mark "struct page" pfns accessed/dirty before dropping mmu_lock

From: Sean Christopherson <[email-masked]>
Date: Mon, 5 Aug 2024 16:53:01 -0700

On Mon, Aug 05, 2024, Oliver Upton wrote:
> > > ---
> > >  arch/arm64/kvm/mmu.c | 10 ++++++----
> > >  1 file changed, 6 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > > index 22ee37360c4e..ce13c3d884d5 100644
> > > --- a/arch/arm64/kvm/mmu.c
> > > +++ b/arch/arm64/kvm/mmu.c
> > > @@ -1685,15 +1685,17 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> > >  	}
> > >  
> > >  out_unlock:
> > > +	if (writable && !ret)
> > > +		kvm_set_pfn_dirty(pfn);
> > 
> > I'm guessing you meant kvm_release_pfn_dirty() here, because this leaks
> > a reference.

Doh, I did indeed.  Alternatively, this could be:

	if (writable && !ret)
		kvm_set_pfn_dirty(pfn);

	kvm_release_pfn_clean(pfn);

It won't matter in the end, because this just becomes:

	kvm_release_faultin_page(kvm, page, !!ret, writable);

So I guess the question is if you prefer to make the switch to an if-else in this
path, or more implicitly in the conversion to kvm_release_faultin_page().

I made the same goof for RISC-V, perhaps to prove that I too can copy+paste arm64's
MMU code ;-)