On Thu, Jun 10, 2021 at 10:46 AM Alper Gun alpergun@google.com wrote:

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

---

arch/x86/kvm/svm/sev.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index e0ce5da97fc2..8d36f0c73071 100644 --- 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;
  

-- 2.32.0.272.g935e593368-goog

Reviewed-by: Marc Orr marcorr@google.com