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

[Paolo Bonzini]

On 10/06/21 19:46, Alper Gun 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@xxxxxxxxxxxxxxx
> Fixes: 59414c989220 ("KVM: SVM: Add support for KVM_SEV_LAUNCH_START command")
> Reported-by: Peter Gonda <pgonda@xxxxxxxxxx>
> Signed-off-by: Alper Gun <alpergun@xxxxxxxxxx>
> ---
>   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;

Queued, thanks.

Paolo