KVM: x86/mmu: Add shadow mask for effective host MTRR memtype

Add shadow_memtype_mask to capture that EPT needs a non-zero memtype mask
instead of relying on TDP being enabled, as NPT doesn't need a non-zero
mask.  This is a glorified nop as kvm_x86_ops.get_mt_mask() returns zero
for NPT anyways.

No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220715230016.3762909-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/spte.c

@@ -33,6 +33,7 @@ u64 __read_mostly shadow_mmio_value;
 u64 __read_mostly shadow_mmio_mask;
 u64 __read_mostly shadow_mmio_access_mask;
 u64 __read_mostly shadow_present_mask;
+u64 __read_mostly shadow_memtype_mask;
 u64 __read_mostly shadow_me_value;
 u64 __read_mostly shadow_me_mask;
 u64 __read_mostly shadow_acc_track_mask;
@@ -161,10 +162,10 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
 
 	if (level > PG_LEVEL_4K)
 		spte |= PT_PAGE_SIZE_MASK;
-	if (tdp_enabled)
-		spte |= static_call(kvm_x86_get_mt_mask)(vcpu, gfn,
-			kvm_is_mmio_pfn(pfn));
 
+	if (shadow_memtype_mask)
+		spte |= static_call(kvm_x86_get_mt_mask)(vcpu, gfn,
+							 kvm_is_mmio_pfn(pfn));
 	if (host_writable)
 		spte |= shadow_host_writable_mask;
 	else
@@ -391,6 +392,13 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
 	shadow_nx_mask		= 0ull;
 	shadow_x_mask		= VMX_EPT_EXECUTABLE_MASK;
 	shadow_present_mask	= has_exec_only ? 0ull : VMX_EPT_READABLE_MASK;
+	/*
+	 * EPT overrides the host MTRRs, and so KVM must program the desired
+	 * memtype directly into the SPTEs.  Note, this mask is just the mask
+	 * of all bits that factor into the memtype, the actual memtype must be
+	 * dynamically calculated, e.g. to ensure host MMIO is mapped UC.
+	 */
+	shadow_memtype_mask	= VMX_EPT_MT_MASK | VMX_EPT_IPAT_BIT;
 	shadow_acc_track_mask	= VMX_EPT_RWX_MASK;
 	shadow_host_writable_mask = EPT_SPTE_HOST_WRITABLE;
 	shadow_mmu_writable_mask  = EPT_SPTE_MMU_WRITABLE;
@@ -441,6 +449,13 @@ void kvm_mmu_reset_all_pte_masks(void)
 	shadow_nx_mask		= PT64_NX_MASK;
 	shadow_x_mask		= 0;
 	shadow_present_mask	= PT_PRESENT_MASK;
+
+	/*
+	 * For shadow paging and NPT, KVM uses PAT entry '0' to encode WB
+	 * memtype in the SPTEs, i.e. relies on host MTRRs to provide the
+	 * correct memtype (WB is the "weakest" memtype).
+	 */
+	shadow_memtype_mask	= 0;
 	shadow_acc_track_mask	= 0;
 	shadow_me_mask		= 0;
 	shadow_me_value		= 0;

arch/x86/kvm/mmu/spte.h

@@ -147,6 +147,7 @@ extern u64 __read_mostly shadow_mmio_value;
 extern u64 __read_mostly shadow_mmio_mask;
 extern u64 __read_mostly shadow_mmio_access_mask;
 extern u64 __read_mostly shadow_present_mask;
+extern u64 __read_mostly shadow_memtype_mask;
 extern u64 __read_mostly shadow_me_value;
 extern u64 __read_mostly shadow_me_mask;