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    SubjectRe: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM
    On Thu, Jan 19, 2023 at 03:25:08PM +0000,
    Sean Christopherson <seanjc@google.com> wrote:

    > On Thu, Jan 19, 2023, Isaku Yamahata wrote:
    > > On Sat, Jan 14, 2023 at 12:37:59AM +0000,
    > > Sean Christopherson <seanjc@google.com> wrote:
    > >
    > > > On Fri, Dec 02, 2022, Chao Peng wrote:
    > > > > This patch series implements KVM guest private memory for confidential
    > > > > computing scenarios like Intel TDX[1]. If a TDX host accesses
    > > > > TDX-protected guest memory, machine check can happen which can further
    > > > > crash the running host system, this is terrible for multi-tenant
    > > > > configurations. The host accesses include those from KVM userspace like
    > > > > QEMU. This series addresses KVM userspace induced crash by introducing
    > > > > new mm and KVM interfaces so KVM userspace can still manage guest memory
    > > > > via a fd-based approach, but it can never access the guest memory
    > > > > content.
    > > > >
    > > > > The patch series touches both core mm and KVM code. I appreciate
    > > > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other
    > > > > reviews are always welcome.
    > > > > - 01: mm change, target for mm tree
    > > > > - 02-09: KVM change, target for KVM tree
    > > >
    > > > A version with all of my feedback, plus reworked versions of Vishal's selftest,
    > > > is available here:
    > > >
    > > > git@github.com:sean-jc/linux.git x86/upm_base_support
    > > >
    > > > It compiles and passes the selftest, but it's otherwise barely tested. There are
    > > > a few todos (2 I think?) and many of the commits need changelogs, i.e. it's still
    > > > a WIP.
    > > >
    > > > As for next steps, can you (handwaving all of the TDX folks) take a look at what
    > > > I pushed and see if there's anything horrifically broken, and that it still works
    > > > for TDX?
    > > >
    > > > Fuad (and pKVM folks) same ask for you with respect to pKVM. Absolutely no rush
    > > > (and I mean that).
    > > >
    > > > On my side, the two things on my mind are (a) tests and (b) downstream dependencies
    > > > (SEV and TDX). For tests, I want to build a lists of tests that are required for
    > > > merging so that the criteria for merging are clear, and so that if the list is large
    > > > (haven't thought much yet), the work of writing and running tests can be distributed.
    > > >
    > > > Regarding downstream dependencies, before this lands, I want to pull in all the
    > > > TDX and SNP series and see how everything fits together. Specifically, I want to
    > > > make sure that we don't end up with a uAPI that necessitates ugly code, and that we
    > > > don't miss an opportunity to make things simpler. The patches in the SNP series to
    > > > add "legacy" SEV support for UPM in particular made me slightly rethink some minor
    > > > details. Nothing remotely major, but something that needs attention since it'll
    > > > be uAPI.
    > >
    > > Although I'm still debuging with TDX KVM, I needed the following.
    > > kvm_faultin_pfn() is called without mmu_lock held. the race to change
    > > private/shared is handled by mmu_seq. Maybe dedicated function only for
    > > kvm_faultin_pfn().
    >
    > Gah, you're not on the other thread where this was discussed[*]. Simply deleting
    > the lockdep assertion is safe, for guest types that rely on the attributes to
    > define shared vs. private, KVM rechecks the attributes under the protection of
    > mmu_seq.
    >
    > I'll get a fixed version pushed out today.
    >
    > [*] https://lore.kernel.org/all/Y8gpl+LwSuSgBFks@google.com

    Now I have tdx kvm working. I've uploaded at the followings.
    It's rebased to v6.2-rc3.
    git@github.com:yamahata/linux.git tdx/upm
    git@github.com:yamahata/qemu.git tdx/upm

    kvm_mmu_do_page_fault() needs the following change.
    kvm_mem_is_private() queries mem_attr_array. kvm_faultin_pfn() also uses
    kvm_mem_is_private(). So the shared-private check in kvm_faultin_pfn() doesn't
    make sense. This change would belong to TDX KVM patches, though.

    diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
    index 72b0da8e27e0..f45ac438bbf4 100644
    --- a/arch/x86/kvm/mmu/mmu_internal.h
    +++ b/arch/x86/kvm/mmu/mmu_internal.h
    @@ -430,7 +430,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
    .max_level = vcpu->kvm->arch.tdp_max_page_level,
    .req_level = PG_LEVEL_4K,
    .goal_level = PG_LEVEL_4K,
    - .is_private = kvm_mem_is_private(vcpu->kvm, cr2_or_gpa >> PAGE_SHIFT),
    + .is_private = kvm_is_private_gpa(vcpu->kvm, cr2_or_gpa),
    };
    int r;

    --
    Isaku Yamahata <isaku.yamahata@gmail.com>

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