Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:5 as permitted sender) client-ip=2620:137:e000::3:5;
MIME-Version: 1.0
References: <cover.1699368322.git.isaku.yamahata@intel.com> <d8b438b6be78b4dbeea5c2a0ecaddfc06bfea43c.1699368322.git.isaku.yamahata@intel.com>
In-Reply-To: <d8b438b6be78b4dbeea5c2a0ecaddfc06bfea43c.1699368322.git.isaku.yamahata@intel.com>
From:   Sagi Shahar <sagis@google.com>
Date:   Fri, 8 Dec 2023 16:26:45 -0800
Message-ID: <CAAhR5DH-k8Jf6tdvpCJPPmHpck=mynvcM4a3We3iNDKzYo3RaA@mail.gmail.com>
Subject: Re: [PATCH v17 093/116] KVM: TDX: Handle TDX PV port io hypercall
To:     isaku.yamahata@intel.com
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        isaku.yamahata@gmail.com, Paolo Bonzini <pbonzini@redhat.com>,
        erdemaktas@google.com, Sean Christopherson <seanjc@google.com>,
        David Matlack <dmatlack@google.com>,
        Kai Huang <kai.huang@intel.com>,
        Zhi Wang <zhi.wang.linux@gmail.com>, chen.bo@intel.com,
        hang.yuan@intel.com, tina.zhang@intel.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Tue, Nov 7, 2023 at 6:58=E2=80=AFAM <isaku.yamahata@intel.com> wrote:
>
> From: Isaku Yamahata <isaku.yamahata@intel.com>
>
> Wire up TDX PV port IO hypercall to the KVM backend function.
>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/kvm/vmx/tdx.c | 57 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 57 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 4e48989d364f..d4b09255ad32 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1140,6 +1140,61 @@ static int tdx_emulate_hlt(struct kvm_vcpu *vcpu)
>         return kvm_emulate_halt_noskip(vcpu);
>  }
>
> +static int tdx_complete_pio_in(struct kvm_vcpu *vcpu)
> +{
> +       struct x86_emulate_ctxt *ctxt =3D vcpu->arch.emulate_ctxt;
> +       unsigned long val =3D 0;
> +       int ret;
> +
> +       WARN_ON_ONCE(vcpu->arch.pio.count !=3D 1);
> +
> +       ret =3D ctxt->ops->pio_in_emulated(ctxt, vcpu->arch.pio.size,
> +                                        vcpu->arch.pio.port, &val, 1);
> +       WARN_ON_ONCE(!ret);
> +
> +       tdvmcall_set_return_code(vcpu, TDG_VP_VMCALL_SUCCESS);
> +       tdvmcall_set_return_val(vcpu, val);
> +
> +       return 1;
> +}
> +
> +static int tdx_emulate_io(struct kvm_vcpu *vcpu)
> +{
> +       struct x86_emulate_ctxt *ctxt =3D vcpu->arch.emulate_ctxt;
> +       unsigned long val =3D 0;
> +       unsigned int port;
> +       int size, ret;
> +       bool write;
> +
> +       ++vcpu->stat.io_exits;
> +
> +       size =3D tdvmcall_a0_read(vcpu);
> +       write =3D tdvmcall_a1_read(vcpu);
> +       port =3D tdvmcall_a2_read(vcpu);
> +
> +       if (size !=3D 1 && size !=3D 2 && size !=3D 4) {
> +               tdvmcall_set_return_code(vcpu, TDG_VP_VMCALL_INVALID_OPER=
AND);
> +               return 1;
> +       }
> +
> +       if (write) {
> +               val =3D tdvmcall_a3_read(vcpu);
> +               ret =3D ctxt->ops->pio_out_emulated(ctxt, size, port, &va=
l, 1);
> +
> +               /* No need for a complete_userspace_io callback. */
> +               vcpu->arch.pio.count =3D 0;
> +       } else {
> +               ret =3D ctxt->ops->pio_in_emulated(ctxt, size, port, &val=
, 1);
> +               if (!ret)
> +                       vcpu->arch.complete_userspace_io =3D tdx_complete=
_pio_in;
> +               else
> +                       tdvmcall_set_return_val(vcpu, val);
> +       }
> +       if (ret)
> +               tdvmcall_set_return_code(vcpu, TDG_VP_VMCALL_SUCCESS);

In the case of a write operation that needs to exit to userspace,
pio_out_emulated is going to return 0 which means that the return code
is never set by tdx_emulate_io.
The reason this code is working now is because r10 is already set to 0
by the guest as part of the call to tdvmcall and never gets written by
the host.

> +       return ret;
> +}
> +
>  static int handle_tdvmcall(struct kvm_vcpu *vcpu)
>  {
>         if (tdvmcall_exit_type(vcpu))
> @@ -1150,6 +1205,8 @@ static int handle_tdvmcall(struct kvm_vcpu *vcpu)
>                 return tdx_emulate_cpuid(vcpu);
>         case EXIT_REASON_HLT:
>                 return tdx_emulate_hlt(vcpu);
> +       case EXIT_REASON_IO_INSTRUCTION:
> +               return tdx_emulate_io(vcpu);
>         default:
>                 break;
>         }
> --
> 2.25.1
>