linux-kernel - Re: [V2 PATCH 1/6] KVM: x86: Add support for testing private memory

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Message-ID: <CAGtprH-Z9=pKM1XxYYQTvwA161BCdgeRbRFQjV=HaV+4Qfo3=w@mail.gmail.com>
Date:   Tue, 17 Jan 2023 14:58:48 -0800
From:   Vishal Annapurve <vannapurve@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
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Subject: Re: [V2 PATCH 1/6] KVM: x86: Add support for testing private memory

On Tue, Jan 17, 2023 at 1:39 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Mon, Dec 05, 2022, Vishal Annapurve wrote:
> > Introduce HAVE_KVM_PRIVATE_MEM_TESTING config to be able to test fd based
> > @@ -272,13 +274,15 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> >               .rsvd = err & PFERR_RSVD_MASK,
> >               .user = err & PFERR_USER_MASK,
> >               .prefetch = prefetch,
> > -             .is_tdp = likely(vcpu->arch.mmu->page_fault == kvm_tdp_page_fault),
> > +             .is_tdp = is_tdp,
> >               .nx_huge_page_workaround_enabled =
> >                       is_nx_huge_page_enabled(vcpu->kvm),
> >
> >               .max_level = KVM_MAX_HUGEPAGE_LEVEL,
> >               .req_level = PG_LEVEL_4K,
> >               .goal_level = PG_LEVEL_4K,
> > +             .is_private = IS_ENABLED(CONFIG_HAVE_KVM_PRIVATE_MEM_TESTING) && is_tdp &&
> > +                             kvm_mem_is_private(vcpu->kvm, cr2_or_gpa >> PAGE_SHIFT),
>
> After looking at the SNP+UPM series, I think we should forego a dedicated Kconfig
> for testing and instead add a new VM type for UPM-capable guests.  The new type,
> e.g. KVM_X86_PROTECTED_VM, can then be used to leverage UPM for "legacy" SEV and
> SEV-ES guests, as well as for UPM-capable guests that don't utilize per-VM
> memory encryption, e.g. KVM selftests.
>
> Carrying test-only behavior is obviously never ideal, and it would pretty much have
> to be mutually exclusive with "real" usage of UPM, otherwise the KVM logics gets
> unnecessarily complex.

Ack, the newly added VM type fits better here with SEV/SEV-ES and
non-confidential selftests being able to share this framework.