[PATCH 5.4] KVM: SVM: Call SEV Guest Decommission if ASID binding fails

* [PATCH 5.4] KVM: SVM: Call SEV Guest Decommission if ASID binding fails
@ 2021-06-28 21:10 Alper Gun
  2021-07-05  7:15 ` Greg KH
  2021-07-08 18:26 ` Greg KH
  0 siblings, 2 replies; 5+ messages in thread
From: Alper Gun @ 2021-06-28 21:10 UTC (permalink / raw)
  To: stable; +Cc: Alper Gun, Peter Gonda, Marc Orr, Paolo Bonzini

commit 934002cd660b035b926438244b4294e647507e13 upstream.

Send SEV_CMD_DECOMMISSION command to PSP firmware if ASID binding
fails. If a failure happens after  a successful LAUNCH_START command,
a decommission command should be executed. Otherwise, guest context
will be unfreed inside the AMD SP. After the firmware will not have
memory to allocate more SEV guest context, LAUNCH_START command will
begin to fail with SEV_RET_RESOURCE_LIMIT error.

The existing code calls decommission inside sev_unbind_asid, but it is
not called if a failure happens before guest activation succeeds. If
sev_bind_asid fails, decommission is never called. PSP firmware has a
limit for the number of guests. If sev_asid_binding fails many times,
PSP firmware will not have resources to create another guest context.

Cc: stable@vger.kernel.org
Fixes: 59414c989220 ("KVM: SVM: Add support for KVM_SEV_LAUNCH_START command")
Reported-by: Peter Gonda <pgonda@google.com>
Signed-off-by: Alper Gun <alpergun@google.com>
Reviewed-by: Marc Orr <marcorr@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210610174604.2554090-1-alpergun@google.com>
---
 arch/x86/kvm/svm.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 074cd170912a..aa2da922ca99 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1794,9 +1794,25 @@ static void sev_asid_free(struct kvm *kvm)
 	__sev_asid_free(sev->asid);
 }
 
-static void sev_unbind_asid(struct kvm *kvm, unsigned int handle)
+static void sev_decommission(unsigned int handle)
 {
 	struct sev_data_decommission *decommission;
+
+	if (!handle)
+		return;
+
+	decommission = kzalloc(sizeof(*decommission), GFP_KERNEL);
+	if (!decommission)
+		return;
+
+	decommission->handle = handle;
+	sev_guest_decommission(decommission, NULL);
+
+	kfree(decommission);
+}
+
+static void sev_unbind_asid(struct kvm *kvm, unsigned int handle)
+{
 	struct sev_data_deactivate *data;
 
 	if (!handle)
@@ -1814,15 +1830,7 @@ static void sev_unbind_asid(struct kvm *kvm, unsigned int handle)
 	sev_guest_df_flush(NULL);
 	kfree(data);
 
-	decommission = kzalloc(sizeof(*decommission), GFP_KERNEL);
-	if (!decommission)
-		return;
-
-	/* decommission handle */
-	decommission->handle = handle;
-	sev_guest_decommission(decommission, NULL);
-
-	kfree(decommission);
+	sev_decommission(handle);
 }
 
 static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
@@ -6475,8 +6483,10 @@ static int sev_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
 
 	/* Bind ASID to this guest */
 	ret = sev_bind_asid(kvm, start->handle, error);
-	if (ret)
+	if (ret) {
+		sev_decommission(start->handle);
 		goto e_free_session;
+	}
 
 	/* return handle to userspace */
 	params.handle = start->handle;
-- 
2.32.0.93.g670b81a890-goog


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