linux-kernel - [PATCH RFC v8 53/56] KVM: SVM: Make VMSAVE target area memory allocation SNP safe

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Message-ID: <20230220183847.59159-54-michael.roth@amd.com>
Date:   Mon, 20 Feb 2023 12:38:44 -0600
From:   Michael Roth <michael.roth@....com>
To:     <kvm@...r.kernel.org>
CC:     <linux-coco@...ts.linux.dev>, <linux-mm@...ck.org>,
        <linux-crypto@...r.kernel.org>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <tglx@...utronix.de>,
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        <alpergun@...gle.com>, <dgilbert@...hat.com>, <jarkko@...nel.org>,
        <ashish.kalra@....com>, <nikunj.dadhania@....com>
Subject: [PATCH RFC v8 53/56] KVM: SVM: Make VMSAVE target area memory allocation SNP safe

From: Ashish Kalra <ashish.kalra@....com>

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 <marcorr@...gle.com>
Signed-off-by: Marc Orr <marcorr@...gle.com>
Reported-by: Alper Gun <alpergun@...gle.com>
Signed-off-by: Ashish Kalra <ashish.kalra@....com>
Signed-off-by: Michael Roth <michael.roth@....com>
---
 arch/x86/kvm/svm/svm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 3fe5f13b5f3a..8bda31a61757 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -665,7 +665,7 @@ 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;
 
-- 
2.25.1