KVM: x86/mmu: Add helpers to return if KVM honors guest MTRRs

Add helpers to check if KVM honors guest MTRRs instead of open coding the
logic in kvm_tdp_page_fault().  Future fixes and cleanups will also need
to determine if KVM should honor guest MTRRs, e.g. for CR0.CD toggling and
and non-coherent DMA transitions.

Provide an inner helper, __kvm_mmu_honors_guest_mtrrs(), so that KVM can
check if guest MTRRs were honored when stopping non-coherent DMA.

Note, there is no need to explicitly check that TDP is enabled, KVM clears
shadow_memtype_mask when TDP is disabled, i.e. it's non-zero if and only
if EPT is enabled.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Link: https://lore.kernel.org/r/20230714065006.20201-1-yan.y.zhao@intel.com
Link: https://lore.kernel.org/r/20230714065043.20258-1-yan.y.zhao@intel.com
[sean: squash into a one patch, drop explicit TDP check massage changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 253fb2093d5d..bb8c86eefac0 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -237,6 +237,13 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
 	return -(u32)fault & errcode;
 }
 
+bool __kvm_mmu_honors_guest_mtrrs(bool vm_has_noncoherent_dma);
+
+static inline bool kvm_mmu_honors_guest_mtrrs(struct kvm *kvm)
+{
+	return __kvm_mmu_honors_guest_mtrrs(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);