KVM: SVM: Call SEV Guest Decommission if ASID binding fails

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>

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index e0ce5da..8d36f0c 100644 (file)
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -199,9 +199,19 @@ static void sev_asid_free(struct kvm_sev_info *sev)
        sev->misc_cg = NULL;
 }
 
-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.handle = handle;
+       sev_guest_decommission(&decommission, NULL);
+}
+
+static void sev_unbind_asid(struct kvm *kvm, unsigned int handle)
+{
        struct sev_data_deactivate deactivate;
 
        if (!handle)
@@ -214,9 +224,7 @@ static void sev_unbind_asid(struct kvm *kvm, unsigned int handle)
        sev_guest_deactivate(&deactivate, NULL);
        up_read(&sev_deactivate_lock);
 
-       /* decommission handle */
-       decommission.handle = handle;
-       sev_guest_decommission(&decommission, NULL);
+       sev_decommission(handle);
 }
 
 static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
@@ -341,8 +349,10 @@ 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;