[PATCH Part2 v6 47/49] *fix for stale per-cpu pointer due to cond_resched during ghcb mapping

Ashish Kalra
2022-06-20T23:20:03Z

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

Signed-off-by: Michael Roth <michael.roth@amd.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