linux-kernel - Re: [PATCH v11 30/35] KVM: x86: Add gmem hook for determining max NPT mapping level

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Date: Mon, 12 Feb 2024 11:03:38 -0600
From: Michael Roth <michael.roth@....com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: <kvm@...r.kernel.org>, <linux-coco@...ts.linux.dev>, <linux-mm@...ck.org>,
	<linux-crypto@...r.kernel.org>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>, <tglx@...utronix.de>, <mingo@...hat.com>,
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	<pankaj.gupta@....com>, <liam.merwick@...cle.com>, <zhi.a.wang@...el.com>
Subject: Re: [PATCH v11 30/35] KVM: x86: Add gmem hook for determining max
 NPT mapping level

On Mon, Feb 12, 2024 at 11:50:26AM +0100, Paolo Bonzini wrote:
> On Sat, Dec 30, 2023 at 6:32 PM Michael Roth <michael.roth@....com> wrote:
> >         int max_order, r;
> > +       u8 max_level;
> >
> >         if (!kvm_slot_can_be_private(fault->slot)) {
> >                 kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
> > @@ -4321,8 +4322,15 @@ static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> >                 return r;
> >         }
> >
> > -       fault->max_level = min(kvm_max_level_for_order(max_order),
> > -                              fault->max_level);
> > +       max_level = kvm_max_level_for_order(max_order);
> > +       r = static_call(kvm_x86_gmem_max_level)(vcpu->kvm, fault->pfn,
> > +                                               fault->gfn, &max_level);
> 
> Might as well pass &fault->max_level directly to the callback, with no
> change to the vendor-specific code.
> 
> I'll include the MMU part in a generic series to be the base for both
> Intel TDX and AMD SEV-SNP, and will do that change.

Sounds good. I'm not sure why I did it that way originally, but what
you're suggesting does seem like it should be equivalent.

-Mike

> 
> Paolo
> 
> > +       if (r) {
> > +               kvm_release_pfn_clean(fault->pfn);
> > +               return r;
> > +       }
> > +
> > +       fault->max_level = min(max_level, fault->max_level);
> >         fault->map_writable = !(fault->slot->flags & KVM_MEM_READONLY);
> >
> >         return RET_PF_CONTINUE;
> > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > index 85f63b6842b6..5eb836b73131 100644
> > --- a/arch/x86/kvm/svm/sev.c
> > +++ b/arch/x86/kvm/svm/sev.c
> > @@ -4315,3 +4315,30 @@ void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end)
> >                 pfn += use_2m_update ? PTRS_PER_PMD : 1;
> >         }
> >  }
> > +
> > +int sev_gmem_max_level(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, u8 *max_level)
> > +{
> > +       int level, rc;
> > +       bool assigned;
> > +
> > +       if (!sev_snp_guest(kvm))
> > +               return 0;
> > +
> > +       rc = snp_lookup_rmpentry(pfn, &assigned, &level);
> > +       if (rc) {
> > +               pr_err_ratelimited("SEV: RMP entry not found: GFN %llx PFN %llx level %d error %d\n",
> > +                                  gfn, pfn, level, rc);
> > +               return -ENOENT;
> > +       }
> > +
> > +       if (!assigned) {
> > +               pr_err_ratelimited("SEV: RMP entry is not assigned: GFN %llx PFN %llx level %d\n",
> > +                                  gfn, pfn, level);
> > +               return -EINVAL;
> > +       }
> > +
> > +       if (level < *max_level)
> > +               *max_level = level;
> > +
> > +       return 0;
> > +}
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> > index f26b8c2a8be4..f745022f7454 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -5067,6 +5067,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
> >         .alloc_apic_backing_page = svm_alloc_apic_backing_page,
> >
> >         .gmem_prepare = sev_gmem_prepare,
> > +       .gmem_max_level = sev_gmem_max_level,
> >         .gmem_invalidate = sev_gmem_invalidate,
> >  };
> >
> > --
> > 2.25.1
> >
>