linux-kernel - [PATCH Part2 v6 47/49] *fix for stale per-cpu pointer due to cond

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Message-ID: <1dbc14735bbc336c171ef8fefd4aef39ddf95816.1655761627.git.ashish.kalra@amd.com>
Date:   Mon, 20 Jun 2022 23:14:58 +0000
From:   Ashish Kalra <Ashish.Kalra@....com>
To:     <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <kvm@...r.kernel.org>, <linux-coco@...ts.linux.dev>,
        <linux-mm@...ck.org>, <linux-crypto@...r.kernel.org>
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        <thomas.lendacky@....com>, <hpa@...or.com>, <ardb@...nel.org>,
        <pbonzini@...hat.com>, <seanjc@...gle.com>, <vkuznets@...hat.com>,
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Subject: [PATCH Part2 v6 47/49] *fix for stale per-cpu pointer due to cond_resched  during ghcb mapping

From: Michael Roth <michael.roth@....com>

Signed-off-by: Michael Roth <michael.roth@....com>
---
 arch/x86/kvm/svm/svm.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index fced6ea423ad..f78e3b1bde0e 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1352,7 +1352,7 @@ static void svm_vcpu_free(struct kvm_vcpu *vcpu)
 static void svm_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
-	struct svm_cpu_data *sd = per_cpu(svm_data, vcpu->cpu);
+	struct svm_cpu_data *sd;
 
 	if (sev_es_guest(vcpu->kvm))
 		sev_es_unmap_ghcb(svm);
@@ -1360,6 +1360,10 @@ static void svm_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 	if (svm->guest_state_loaded)
 		return;
 
+	/* sev_es_unmap_ghcb() can resched, so grab per-cpu pointer afterward. */
+	barrier();
+	sd = per_cpu(svm_data, vcpu->cpu);
+
 	/*
 	 * Save additional host state that will be restored on VMEXIT (sev-es)
 	 * or subsequent vmload of host save area.
-- 
2.25.1