[PATCH 6.12.y 3/3] KVM: SEV: Mark vCPU RUNNABLE after AP_CREATE, even if VMSA is unusable

[Sasha Levin <sashal@kernel.org>]

From: Sean Christopherson <seanjc@google.com>

[ Upstream commit 98ade8c48c28c227fe2e80e545ff0c57cd4712a3 ]

Always mark the vCPU as RUNNABLE after responding to AP_CREATE, even if the
guest-specified VMSA is unusable, e.g. isn't backed by a memslot or doesn't
have a backing guest_memfd page.  If the VMSA is unusable, leaving the vCPU
in a non-running state will effectively hang the vCPU instead of reporting
an error to userspace.  This will also allow retrying the VMSA load in the
future, to fix a bug where KVM doesn't honor guest_memfd invalidation
events, e.g. if AP_CREATION races with PUNCH_HOLE.

Cc: stable@vger.kernel.org # 6.12.x
Reviewed-by: Michael Roth <michael.roth@amd.com>
Link: https://patch.msgid.link/20260709204948.1988414-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/svm/sev.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 7be27b481ca22..bf89f4d6e2e78 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3962,9 +3962,6 @@ static void sev_snp_reload_vmsa(struct kvm_vcpu *vcpu, gpa_t gpa)
 	svm->sev_es.snp_guest_vmsa_gpa = gpa;
 	svm->vmcb->control.vmsa_pa = pfn_to_hpa(pfn);
 
-	/* Mark the vCPU as runnable */
-	kvm_set_mp_state(vcpu, KVM_MP_STATE_RUNNABLE);
-
 	/*
 	 * gmem pages aren't currently migratable, but if this ever changes
 	 * then care should be taken to ensure svm->sev_es.vmsa is pinned
@@ -3999,6 +3996,15 @@ void sev_snp_init_protected_guest_state(struct kvm_vcpu *vcpu)
 	svm->sev_es.snp_pending_vmsa_gpa = INVALID_PAGE;
 
 	sev_snp_reload_vmsa(vcpu, gpa);
+
+	/*
+	 * Mark the vCPU as runnable for CREATE requests, indicated by a valid
+	 * VMSA GPA, even if installing the VMSA failed, so that KVM_RUN will
+	 * fail instead of blocking indefinitely and hanging the vCPU, e.g. if
+	 * the backing guest_memfd page is unavailable.
+	 */
+	if (VALID_PAGE(gpa))
+		kvm_set_mp_state(vcpu, KVM_MP_STATE_RUNNABLE);
 }
 
 #undef kvm_set_mp_state
-- 
2.53.0