[PATCH v2] KVM: SVM: fix missing sev_decommission() in sev_receive_start()

[Mingwei Zhang <mizhang@google.com>]

DECOMMISSION the current SEV context if binding an ASID fails after
RECEIVE_START. Per AMD's SEV API, RECEIVE_START generates a new guest
context and thus needs to be paired with DECOMMISSION:

AMD SEV API v0.24 Section 1.3.3

  "The RECEIVE_START command is the only command other than the
  LAUNCH_START command that generates a new guest context and guest
  handle."

The missing DECOMMISSION can result in subsequent SEV launch failures due
to insufficient resource. In particular, both LAUNCH_START and
RECEIVE_START command will fail with SEV_RET_RESOURCE_LIMIT error.

Note, LAUNCH_START suffered from the same bug, but was previously fixed by
[1]. However, the same bug could come back to LAUNCH_START if RECEIVE_START
part was not fixed.

So add the sev_decommission() function in sev_receive_start.

[1] commit 934002cd660b ("KVM: SVM: Call SEV Guest Decommission if ASID
			 binding fails").

Cc: Alper Gun <alpergun@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: David Rienjes <rientjes@google.com>
Cc: Marc Orr <marcorr@google.com>
Cc: John Allen <john.allen@amd.com>
Cc: Peter Gonda <pgonda@google.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Vipin Sharma <vipinsh@google.com>

Reviewed-by: Marc Orr <marcorr@google.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Acked-by: Brijesh Singh <brijesh.singh@amd.com>
Fixes: af43cbbf954b ("KVM: SVM: Add support for KVM_SEV_RECEIVE_START command")
Signed-off-by: Mingwei Zhang <mizhang@google.com>
---
 arch/x86/kvm/svm/sev.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 75e0b21ad07c..55d8b9c933c3 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1397,8 +1397,10 @@ static int sev_receive_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;
+	}
 
 	params.handle = start.handle;
 	if (copy_to_user((void __user *)(uintptr_t)argp->data,
-- 
2.33.0.464.g1972c5931b-goog