Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
MIME-Version: 1.0
References: <20220321150214.1895231-1-pgonda@google.com>
In-Reply-To: <20220321150214.1895231-1-pgonda@google.com>
From:   Marc Orr <marcorr@google.com>
Date:   Mon, 21 Mar 2022 10:25:22 -0700
Message-ID: <CAA03e5HEKPxfGZ57r=intg_ogTp_JPAio36QJXqviMZM_KmvEg@mail.gmail.com>
Subject: Re: [PATCH] Add KVM_EXIT_SHUTDOWN metadata for SEV-ES
To:     Peter Gonda <pgonda@google.com>
Cc:     kvm list <kvm@vger.kernel.org>, Borislav Petkov <bp@alien8.de>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Brijesh Singh <brijesh.singh@amd.com>,
        Joerg Roedel <jroedel@suse.de>,
        Sean Christopherson <seanjc@google.com>,
        LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Mon, Mar 21, 2022 at 8:02 AM Peter Gonda <pgonda@google.com> wrote:
>
> SEV-ES guests can request termination using the GHCB's MSR protocol. See
> AMD's GHCB spec section '4.1.13 Termination Request'. Currently when a
> guest does this the userspace VMM sees an KVM_EXIT_UNKNOWN (-EVINAL)
> return code from KVM_RUN. By adding a KVM_EXIT_SHUTDOWN_ENTRY to kvm_run
> struct the userspace VMM can clearly see the guest has requested a SEV-ES
> termination including the termination reason code set and reason code.
>
> Signed-off-by: Peter Gonda <pgonda@google.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Cc: Joerg Roedel <jroedel@suse.de>
> Cc: Marc Orr <marcorr@google.com>
> Cc: Sean Christopherson <seanjc@google.com>
> Cc: kvm@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
>
> ---
>
> Tested by making an SEV-ES guest call sev_es_terminate() with hardcoded
> reason code set and reason code and then observing the codes from the
> userspace VMM in the kvm_run.shutdown.data fields.
>
> ---
>  arch/x86/kvm/svm/sev.c   |  9 +++++++--
>  include/uapi/linux/kvm.h | 12 ++++++++++++
>  2 files changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 75fa6dd268f0..5f9d37dd3f6f 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2735,8 +2735,13 @@ static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
>                 pr_info("SEV-ES guest requested termination: %#llx:%#llx\n",
>                         reason_set, reason_code);
>
> -               ret = -EINVAL;
> -               break;
> +               vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
> +               vcpu->run->shutdown.reason = KVM_SHUTDOWN_SEV_TERM;
> +               vcpu->run->shutdown.ndata = 2;
> +               vcpu->run->shutdown.data[0] = reason_set;
> +               vcpu->run->shutdown.data[1] = reason_code;
> +
> +               return 0;

Maybe I'm missing something, but don't we want to keep returning an error?

rationale: Current behavior: return -EINVAL to userpsace, but
userpsace cannot infer where the -EINVAL came from. After this patch:
We should still return -EINVAL to userspace, but now userspace can
parse this new info in the KVM run struct to properly terminate.

>         }
>         default:
>                 /* Error, keep GHCB MSR value as-is */
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 8616af85dc5d..12138b8f290c 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -271,6 +271,12 @@ struct kvm_xen_exit {
>  #define KVM_EXIT_XEN              34
>  #define KVM_EXIT_RISCV_SBI        35
>
> +/* For KVM_EXIT_SHUTDOWN */
> +/* Standard VM shutdown request. No additional metadata provided. */
> +#define KVM_SHUTDOWN_REQ       0
> +/* SEV-ES termination request */
> +#define KVM_SHUTDOWN_SEV_TERM  1
> +
>  /* For KVM_EXIT_INTERNAL_ERROR */
>  /* Emulate instruction failed. */
>  #define KVM_INTERNAL_ERROR_EMULATION   1
> @@ -311,6 +317,12 @@ struct kvm_run {
>                 struct {
>                         __u64 hardware_exit_reason;
>                 } hw;
> +               /* KVM_EXIT_SHUTDOWN_ENTRY */
> +               struct {
> +                       __u64 reason;
> +                       __u32 ndata;
> +                       __u64 data[16];
> +               } shutdown;
>                 /* KVM_EXIT_FAIL_ENTRY */
>                 struct {
>                         __u64 hardware_entry_failure_reason;
> --
> 2.35.1.894.gb6a874cedc-goog
>