On 25/06/21 00:02, Alper Gun wrote:

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

---

arch/x86/kvm/svm/sev.c | 26 +++++++++++++++----------- 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index dbc6214d69de..96a61fab9c58 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -143,9 +143,19 @@ 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) @@ -165,15 +175,7 @@ static void sev_unbind_asid(struct kvm *kvm, unsigned int handle) 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 int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp) @@ -303,8 +305,10 @@ 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;

Oops, NACK. Sorry. You need to preserve the kzalloc in older versions of Linux.

Paolo