[v13,21/26] KVM: SEV: Avoid WBINVD for HVA-based MMU notifications for SNP

Commit Message

Michael Roth April 18, 2024, 7:41 p.m. UTC

From: Ashish Kalra <[e-mail]>

With SNP/guest_memfd, private/encrypted memory should not be mappable,
and MMU notifications for HVA-mapped memory will only be relevant to
unencrypted guest memory. Therefore, the rationale behind issuing a
wbinvd_on_all_cpus() in sev_guest_memory_reclaimed() should not apply
for SNP guests and can be ignored.

Signed-off-by: Ashish Kalra <[e-mail]>
Reviewed-by: Paolo Bonzini <[e-mail]>
[mdr: Add some clarifications in commit]
Signed-off-by: Michael Roth <[e-mail]>
---
 arch/x86/kvm/svm/sev.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

Patch

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 3fabd1ee718f..03bfb7b9732d 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3033,7 +3033,14 @@  static void sev_flush_encrypted_page(struct kvm_vcpu *vcpu, void *va)
 
 void sev_guest_memory_reclaimed(struct kvm *kvm)
 {
-	if (!sev_guest(kvm))
+	/*
+	 * With SNP+gmem, private/encrypted memory should be
+	 * unreachable via the hva-based mmu notifiers. Additionally,
+	 * for shared->private translations, H/W coherency will ensure
+	 * first guest access to the page would clear out any existing
+	 * dirty copies of that cacheline.
+	 */
+	if (!sev_guest(kvm) || sev_snp_guest(kvm))
 		return;
 
 	wbinvd_on_all_cpus();