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

BugLink: https://bugs.launchpad.net/bugs/1936245
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 0e3ebb01fcc72505230fd84b4d59c6dde290edde..54de32d1c05242ad06ff4fe44c3b64e09690f358 100644 (file)
--- 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,
@@ -6476,8 +6484,10 @@ 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;