From: Alper Gun <alpergun@google.com>
Date: Thu, 10 Jun 2021 17:46:04 +0000
Subject: KVM: SVM: Call SEV Guest Decommission if ASID binding fails
Git-commit: 934002cd660b035b926438244b4294e647507e13
Patch-mainline: v5.13-rc7
References: 12sp5

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>

Acked-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/kvm/svm.c |   26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1739,9 +1739,19 @@ static void sev_asid_free(int asid)
 	mutex_unlock(&sev_bitmap_lock);
 }
 
+static void sev_decommission(unsigned int handle)
+{
+	struct sev_data_decommission decommission;
+
+	if (!handle)
+		return;
+
+	decommission.handle = handle;
+	sev_guest_decommission(&decommission, NULL);
+}
+
 static void sev_unbind_asid(struct kvm *kvm, unsigned int handle)
 {
-	struct sev_data_decommission *decommission;
 	struct sev_data_deactivate *data;
 
 	if (!handle)
@@ -1769,15 +1779,7 @@ static void sev_unbind_asid(struct kvm *
 
 	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,
@@ -6412,8 +6414,10 @@ static int sev_launch_start(struct kvm *
 
 	/* 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;