Subject: Re: [RFC PATCH v12 02/33] KVM: Use gfn instead of hva for mmu_notifier_retry

From: Sean Christopherson <[email-masked]>
Date: Wed, 20 Sep 2023 06:55:05 -0700

On Wed, Sep 20, 2023, Xu Yilun wrote:
> On 2023-09-13 at 18:55:00 -0700, Sean Christopherson wrote:
> > +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > +{
> > +	lockdep_assert_held_write(&kvm->mmu_lock);
> > +
> > +	WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > +
> >  	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> >  		kvm->mmu_invalidate_range_start = start;
> >  		kvm->mmu_invalidate_range_end = end;
> 
> IIUC, Now we only add or override a part of the invalidate range in
> these fields, IOW only the range in last slot is stored when we unlock.

Ouch.  Good catch!

> That may break mmu_invalidate_retry_gfn() cause it can never know the
> whole invalidate range.
> 
> How about we extend the mmu_invalidate_range_start/end everytime so that
> it records the whole invalidate range:
> 
> if (kvm->mmu_invalidate_range_start == INVALID_GPA) {
> 	kvm->mmu_invalidate_range_start = start;
> 	kvm->mmu_invalidate_range_end = end;
> } else {
> 	kvm->mmu_invalidate_range_start =
> 		min(kvm->mmu_invalidate_range_start, start);
> 	kvm->mmu_invalidate_range_end =
> 		max(kvm->mmu_invalidate_range_end, end);
> }

Yeah, that does seem to be the easiest solution.

I'll post a fixup patch, unless you want the honors.