Re: [PATCH RFC v7 01/64] KVM: Fix memslot boundary condition for large page

[Chao Peng]

On Wed, Jan 04, 2023 at 12:01:05PM +0000, Jarkko Sakkinen wrote:
> On Wed, Dec 14, 2022 at 01:39:53PM -0600, Michael Roth wrote:
> > From: Nikunj A Dadhania <nikunj@xxxxxxx>
> > 
> > Aligned end boundary causes a kvm crash, handle the case.
> > 
> 
> Link: https://lore.kernel.org/kvm/20221202061347.1070246-8-chao.p.peng@xxxxxxxxxxxxxxx/
> 
> Chao, are you aware of this issue already?

Thanks Jarkko adding me. I'm not aware of there is a fix.

> 
> > Signed-off-by: Nikunj A Dadhania <nikunj@xxxxxxx>
> > Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
> > ---
> >  arch/x86/kvm/mmu/mmu.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index b1953ebc012e..b3ffc61c668c 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -7159,6 +7159,9 @@ static void kvm_update_lpage_private_shared_mixed(struct kvm *kvm,
> >  		for (gfn = first + pages; gfn < last; gfn += pages)
> >  			linfo_set_mixed(gfn, slot, level, false);
> >  
> > +		if (gfn == last)
> > +			goto out;
> > +

Nikunj or Michael, could you help me understand in which case it causes
a KVM crash? To me, even the end is aligned to huge page boundary, but:
    last = (end - 1) & mask;
so 'last' is the base address for the last effective huage page. Even
when gfn == last, it should still a valid page and needs to be updated
for mem_attrs, correct?

Thanks,
Chao
> >  		gfn = last;
> >  		gfn_end = min(last + pages, slot->base_gfn + slot->npages);
> >  		mixed = mem_attrs_mixed(kvm, slot, level, attrs, gfn, gfn_end);
> > -- 
> > 2.25.1
> > 
> 
> 
> BR, Jarkko