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    Subject[PATCH v3 01/11] KVM: x86/mmu: helpers to return if KVM honors guest MTRRs
    Date
    Added helpers to check if KVM honors guest MTRRs.
    The inner helper __kvm_mmu_honors_guest_mtrrs() is also provided to
    outside callers for the purpose of checking if guest MTRRs were honored
    before stopping non-coherent DMA.

    Suggested-by: Sean Christopherson <seanjc@google.com>
    Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
    ---
    arch/x86/kvm/mmu.h | 7 +++++++
    arch/x86/kvm/mmu/mmu.c | 15 +++++++++++++++
    2 files changed, 22 insertions(+)

    diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
    index 92d5a1924fc1..38bd449226f6 100644
    --- a/arch/x86/kvm/mmu.h
    +++ b/arch/x86/kvm/mmu.h
    @@ -235,6 +235,13 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
    return -(u32)fault & errcode;
    }

    +bool __kvm_mmu_honors_guest_mtrrs(struct kvm *kvm, bool vm_has_noncoherent_dma);
    +
    +static inline bool kvm_mmu_honors_guest_mtrrs(struct kvm *kvm)
    +{
    + return __kvm_mmu_honors_guest_mtrrs(kvm, kvm_arch_has_noncoherent_dma(kvm));
    +}
    +
    void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end);

    int kvm_arch_write_log_dirty(struct kvm_vcpu *vcpu);
    diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
    index 1e5db621241f..b4f89f015c37 100644
    --- a/arch/x86/kvm/mmu/mmu.c
    +++ b/arch/x86/kvm/mmu/mmu.c
    @@ -4516,6 +4516,21 @@ static int kvm_tdp_mmu_page_fault(struct kvm_vcpu *vcpu,
    }
    #endif

    +bool __kvm_mmu_honors_guest_mtrrs(struct kvm *kvm, bool vm_has_noncoherent_dma)
    +{
    + /*
    + * If the TDP is enabled, the host MTRRs are ignored by TDP
    + * (shadow_memtype_mask is non-zero), and the VM has non-coherent DMA
    + * (DMA doesn't snoop CPU caches), KVM's ABI is to honor the memtype
    + * from the guest's MTRRs so that guest accesses to memory that is
    + * DMA'd aren't cached against the guest's wishes.
    + *
    + * Note, KVM may still ultimately ignore guest MTRRs for certain PFNs,
    + * e.g. KVM will force UC memtype for host MMIO.
    + */
    + return vm_has_noncoherent_dma && tdp_enabled && shadow_memtype_mask;
    +}
    +
    int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
    {
    /*
    --
    2.17.1
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