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>

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 253fb2093d5dadcbe7994a004c26e2ad54a054a7..bb8c86eefac047de05f25c937fafd66f7e2ebe6a 100644 (file)
--- 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);

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index f7901cb4d2fa4b67a4dae93648a169fd2931585b..5d3dc7119e57df0d523d3f3bf92b5bce2d86a4a8 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4479,21 +4479,28 @@ out_unlock:
 }
 #endif
 
-int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
+bool __kvm_mmu_honors_guest_mtrrs(bool vm_has_noncoherent_dma)
 {
        /*
-        * If the guest's MTRRs may be used to compute the "real" memtype,
-        * restrict the mapping level to ensure KVM uses a consistent memtype
-        * across the entire mapping.  If 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.
+        * If host MTRRs are ignored (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.
         */
-       if (shadow_memtype_mask && kvm_arch_has_noncoherent_dma(vcpu->kvm)) {
+       return vm_has_noncoherent_dma && shadow_memtype_mask;
+}
+
+int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
+{
+       /*
+        * If the guest's MTRRs may be used to compute the "real" memtype,
+        * restrict the mapping level to ensure KVM uses a consistent memtype
+        * across the entire mapping.
+        */
+       if (kvm_mmu_honors_guest_mtrrs(vcpu->kvm)) {
                for ( ; fault->max_level > PG_LEVEL_4K; --fault->max_level) {
                        int page_num = KVM_PAGES_PER_HPAGE(fault->max_level);
                        gfn_t base = gfn_round_for_level(fault->gfn,