[PATCH 4.19 30/34] KVM: SVM: Call SEV Guest Decommission if ASID binding fails

Greg Kroah-Hartman
2021-07-09T13:22:14Z

From: Alper Gun <alpergun@google.com>

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>

---
arch/x86/kvm/svm.c | 32 +++++++++++++++++++++-----------
1 file changed, 21 insertions(+), 11 deletions(-)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1791,9 +1791,25 @@ static void sev_asid_free(struct kvm *kv
__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)
@@ -1811,15 +1827,7 @@ static void sev_unbind_asid(struct kvm *
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,
@@ -6469,8 +6477,10 @@ 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;