linux-kernel - Re: [PATCH v19 109/130] KVM: TDX: Handle TDX PV port io hypercall

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Message-ID: <20240716211944.GC1900928@ls.amr.corp.intel.com>
Date: Tue, 16 Jul 2024 14:19:44 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: Isaku Yamahata <isaku.yamahata@...el.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
	isaku.yamahata@...ux.intel.com,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Reinette Chatre <reinette.chatre@...el.com>
Subject: Re: [PATCH v19 109/130] KVM: TDX: Handle TDX PV port io hypercall

On Tue, Jul 09, 2024 at 02:26:35PM +0800,
Binbin Wu <binbin.wu@...ux.intel.com> wrote:

> 
> 
> On 4/18/2024 4:10 AM, Isaku Yamahata wrote:
> > On Wed, Apr 17, 2024 at 08:51:39PM +0800,
> > Binbin Wu <binbin.wu@...ux.intel.com> wrote:
> > 
> > > 
> > > On 2/26/2024 4:26 PM, isaku.yamahata@...el.com wrote:
> > > > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > > > 
> > > > Wire up TDX PV port IO hypercall to the KVM backend function.
> > > > 
> > > > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > > > Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
> > > > ---
> > > > v18:
> > > > - Fix out case to set R10 and R11 correctly when user space handled port
> > > >     out.
> > > > ---
> > > >    arch/x86/kvm/vmx/tdx.c | 67 ++++++++++++++++++++++++++++++++++++++++++
> > > >    1 file changed, 67 insertions(+)
> > > > 
> > > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > > > index a2caf2ae838c..55fc6cc6c816 100644
> > > > --- a/arch/x86/kvm/vmx/tdx.c
> > > > +++ b/arch/x86/kvm/vmx/tdx.c
> > > > @@ -1152,6 +1152,71 @@ static int tdx_emulate_hlt(struct kvm_vcpu *vcpu)
> > > >    	return kvm_emulate_halt_noskip(vcpu);
> > > >    }
> > > > +static int tdx_complete_pio_out(struct kvm_vcpu *vcpu)
> > > > +{
> > > > +	tdvmcall_set_return_code(vcpu, TDVMCALL_SUCCESS);
> > > > +	tdvmcall_set_return_val(vcpu, 0);
> > > > +	return 1;
> > > > +}
> > > > +
> > > > +static int tdx_complete_pio_in(struct kvm_vcpu *vcpu)
> > > > +{
> > > > +	struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
> > > > +	unsigned long val = 0;
> > > > +	int ret;
> > > > +
> > > > +	WARN_ON_ONCE(vcpu->arch.pio.count != 1);
> > > > +
> > > > +	ret = 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, TDVMCALL_SUCCESS);
> > > > +	tdvmcall_set_return_val(vcpu, val);
> > > > +
> > > > +	return 1;
> > > > +}
> > > > +
> > > > +static int tdx_emulate_io(struct kvm_vcpu *vcpu)
> > > > +{
> > > > +	struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
> > > > +	unsigned long val = 0;
> > > > +	unsigned int port;
> > > > +	int size, ret;
> > > > +	bool write;
> > > > +
> > > > +	++vcpu->stat.io_exits;
> > > > +
> > > > +	size = tdvmcall_a0_read(vcpu);
> > > > +	write = tdvmcall_a1_read(vcpu);
> > > > +	port = tdvmcall_a2_read(vcpu);
> > > > +
> > > > +	if (size != 1 && size != 2 && size != 4) {
> > > > +		tdvmcall_set_return_code(vcpu, TDVMCALL_INVALID_OPERAND);
> > > > +		return 1;
> > > > +	}
> > > > +
> > > > +	if (write) {
> > > > +		val = tdvmcall_a3_read(vcpu);
> > > > +		ret = ctxt->ops->pio_out_emulated(ctxt, size, port, &val, 1);
> > > > +
> > > > +		/* No need for a complete_userspace_io callback. */
> > > I am confused about the comment.
> > > 
> > > The code below sets the complete_userspace_io callback for write case,
> > > i.e. tdx_complete_pio_out().
> > You're correct. This comment is stale and should be removed it.
> Also, since the tdx_complete_pio_out() is installed as complete_userspace_io
> callback for write, it's more reasonable to move the reset of pio.count into
> tdx_complete_pio_out().
> How about the following fixup:

It makes sense. It matches better with other complete callbacks
for tdx_complete_pio_out() to clear pio.count to 0.


> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 9ead46cb75ab..b43bb8ccddb9 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1115,6 +1115,7 @@ static int tdx_emulate_hlt(struct kvm_vcpu *vcpu)
> 
>  static int tdx_complete_pio_out(struct kvm_vcpu *vcpu)
>  {
> +       vcpu->arch.pio.count = 0;
>         tdvmcall_set_return_code(vcpu, TDVMCALL_SUCCESS);
>         tdvmcall_set_return_val(vcpu, 0);
>         return 1;
> @@ -1159,15 +1160,13 @@ static int tdx_emulate_io(struct kvm_vcpu *vcpu)
>         if (write) {
>                 val = tdvmcall_a3_read(vcpu);
>                 ret = ctxt->ops->pio_out_emulated(ctxt, size, port, &val,
> 1);
> -
> -               /* No need for a complete_userspace_io callback. */
> -               vcpu->arch.pio.count = 0;
> -       } else
> +       } else {
>                 ret = ctxt->ops->pio_in_emulated(ctxt, size, port, &val, 1);
> +       }
> 
> -       if (ret)
> +       if (ret) {
>                 tdvmcall_set_return_val(vcpu, val);
> -       else {
> +       } else {
>                 if (write)
>                         vcpu->arch.complete_userspace_io =
> tdx_complete_pio_out;
>                 else
> 
> 

-- 
Isaku Yamahata <isaku.yamahata@...el.com>