KVM: SVM: Flush when freeing encrypted pages even on SME_COHERENT CPUs

Use clflush_cache_range() to flush the confidential memory when
SME_COHERENT is supported in AMD CPU. Cache flush is still needed since
SME_COHERENT only support cache invalidation at CPU side. All confidential
cache lines are still incoherent with DMA devices.

Cc: stable@vger.kerel.org

Fixes: add5e2f0 ("KVM: SVM: Add support for the SEV-ES VMSA")
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
Message-Id: <20220421031407.2516575-3-mizhang@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/sev.c

@@ -2239,11 +2239,14 @@ static void sev_flush_encrypted_page(struct kvm_vcpu *vcpu, void *va)
 	unsigned long addr = (unsigned long)va;
 
 	/*
-	 * If hardware enforced cache coherency for encrypted mappings of the
-	 * same physical page is supported, nothing to do.
+	 * If CPU enforced cache coherency for encrypted mappings of the
+	 * same physical page is supported, use CLFLUSHOPT instead. NOTE: cache
+	 * flush is still needed in order to work properly with DMA devices.
 	 */
-	if (boot_cpu_has(X86_FEATURE_SME_COHERENT))
+	if (boot_cpu_has(X86_FEATURE_SME_COHERENT)) {
+		clflush_cache_range(va, PAGE_SIZE);
 		return;
+	}
 
 	/*
 	 * VM Page Flush takes a host virtual address and a guest ASID.  Fall