[RFC,v7,61/64] KVM: SVM: Make VMSAVE target area memory allocation SNP safe

Commit Message

Michael Roth Dec. 14, 2022, 7:40 p.m. UTC

From: Ashish Kalra <[e-mail]>

Implement a workaround for an SNP erratum where the CPU will incorrectly
signal an RMP violation #PF if a hugepage (2mb or 1gb) collides with the
RMP entry of the VMSAVE target page.

When SEV-SNP is globally enabled, the CPU marks the VMSAVE target page
as "InUse" while the VMSAVE instruction is executing. If another
CPU writes to a different page in the same 2MB region while the VMSAVE
is executing, the CPU will throw an RMP violation #PF.

Use the snp safe generic allocator for allocating the VMSA target
page which will ensure that the page returned is not a hugepage, as it
is already being used for the allocating the VMCB, VMSA and AVIC backing
page.

Co-developed-by: Marc Orr <[e-mail]>
Signed-off-by: Marc Orr <[e-mail]>
Reported-by: Alper Gun <[e-mail]>
Signed-off-by: Ashish Kalra <[e-mail]>
Signed-off-by: Michael Roth <[e-mail]>
---
 arch/x86/kvm/svm/svm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 543261c87eb3..1d4a723d5def 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -653,7 +653,7 @@  static int svm_cpu_init(int cpu)
 	int ret = -ENOMEM;
 
 	memset(sd, 0, sizeof(struct svm_cpu_data));
-	sd->save_area = alloc_page(GFP_KERNEL | __GFP_ZERO);
+	sd->save_area = snp_safe_alloc_page(NULL);
 	if (!sd->save_area)
 		return ret;