[PATCH 5.15 110/124] KVM: SVM: Flush when freeing encrypted pages even on SME_COHERENT CPUs

Greg Kroah-Hartman
2022-04-26T09:17:22Z

From: Mingwei Zhang <mizhang@google.com>

commit d45829b351ee6ec5f54dd55e6aca1f44fe239fe6 upstream.

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: add5e2f04541 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/svm/sev.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1990,11 +1990,14 @@ static void sev_flush_guest_memory(struc
unsigned long len)
{
/*
- * 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;
+ }

/*
* If the VM Page Flush MSR is supported, use it to flush the page