[PATCH 5.10 v2] KVM: SVM: Call SEV Guest Decommission if ASID binding fails

[PATCH 5.10 v2] KVM: SVM: Call SEV Guest Decommission if ASID binding fails

[Alper Gun]

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 | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 16b10b9436dc..01547bdbfb06 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -130,9 +130,25 @@ static void sev_asid_free(int asid)
 	mutex_unlock(&sev_bitmap_lock);
 }
 
-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)
@@ -152,15 +168,7 @@ 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)
@@ -288,8 +296,10 @@ 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;
-- 
2.32.0.93.g670b81a890-goog

Re: [PATCH 5.10 v2] KVM: SVM: Call SEV Guest Decommission if ASID binding fails

[Paolo Bonzini]

On 25/06/21 01:48, 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 | 32 +++++++++++++++++++++-----------
>   1 file changed, 21 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 16b10b9436dc..01547bdbfb06 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -130,9 +130,25 @@ static void sev_asid_free(int asid)
>   	mutex_unlock(&sev_bitmap_lock);
>   }
>   
> -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)
> @@ -152,15 +168,7 @@ 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)
> @@ -288,8 +296,10 @@ 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;
> 

Acked-by: Paolo Bonzini <pbonzini@redhat.com>