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    SubjectRe: [PATCH 02/10] KVM: SVM: Use AVIC_HPA_MASK when initializing vCPU's Physical ID entry
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    У вт, 2023-08-15 у 14:35 -0700, Sean Christopherson пише:
    > Use AVIC_HPA_MASK instead of AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK when
    > initializing a vCPU's Physical ID table entry, the two masks are identical.

    Masks are identical, but they refer to different things.
    AVIC_HPA_MASK is about avic's fields in vmcb, while AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK
    is about the portion of the physical id entry which has the address.

    They are the same currently but for documentation purposes I don't understand
    why removal of one of them makes sense.

    IMHO, it's best to define them to the same value, e.g:

    #define AVIC_HPA_MASK GENMASK_ULL(51, 12)

    #define AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK GENMASK_ULL(51, 12)

    Best regards,
    Maxim Levitsky


    > Keep both #defines for now, along with a few new static asserts. A future
    > change will clean up the entire mess (spoiler alert, the masks are
    > pointless).
    >
    > Opportunisitically move the bitwise-OR of AVIC_PHYSICAL_ID_ENTRY_VALID_MASK
    > outside of the call to __sme_set(), again to pave the way for code
    > deduplication. __sme_set() is purely additive, i.e. ORing in the valid
    > bit before or after the C-bit does not change the end result.
    >
    > No functional change intended.
    >
    > Signed-off-by: Sean Christopherson <seanjc@google.com>
    > ---
    > arch/x86/include/asm/svm.h | 2 ++
    > arch/x86/kvm/svm/avic.c | 5 ++---
    > 2 files changed, 4 insertions(+), 3 deletions(-)
    >
    > diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
    > index 1e70600e84f7..609c9b596399 100644
    > --- a/arch/x86/include/asm/svm.h
    > +++ b/arch/x86/include/asm/svm.h
    > @@ -285,6 +285,8 @@ static_assert((AVIC_MAX_PHYSICAL_ID & AVIC_PHYSICAL_MAX_INDEX_MASK) == AVIC_MAX_
    > static_assert((X2AVIC_MAX_PHYSICAL_ID & AVIC_PHYSICAL_MAX_INDEX_MASK) == X2AVIC_MAX_PHYSICAL_ID);
    >
    > #define AVIC_HPA_MASK ~((0xFFFULL << 52) | 0xFFF)
    > +static_assert(AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK == AVIC_HPA_MASK);
    > +static_assert(AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK == GENMASK_ULL(51, 12));
    >
    > #define SVM_SEV_FEAT_DEBUG_SWAP BIT(5)
    >
    > diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
    > index 7062164e4041..442c58ef8158 100644
    > --- a/arch/x86/kvm/svm/avic.c
    > +++ b/arch/x86/kvm/svm/avic.c
    > @@ -308,9 +308,8 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu)
    > if (!entry)
    > return -EINVAL;
    >
    > - new_entry = __sme_set((page_to_phys(svm->avic_backing_page) &
    > - AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK) |
    > - AVIC_PHYSICAL_ID_ENTRY_VALID_MASK);
    > + new_entry = __sme_set(page_to_phys(svm->avic_backing_page) & AVIC_HPA_MASK) |
    > + AVIC_PHYSICAL_ID_ENTRY_VALID_MASK;
    > WRITE_ONCE(*entry, new_entry);
    >
    > svm->avic_physical_id_cache = entry;






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