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

[Binbin Wu]

On 4/18/2024 4:10 AM, Isaku Yamahata wrote:
> On Wed, Apr 17, 2024 at 08:51:39PM +0800,
> Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx> wrote:
>
> > On 2/26/2024 4:26 PM, isaku.yamahata@xxxxxxxxx wrote:
> > > From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> > >
> > > Wire up TDX PV port IO hypercall to the KVM backend function.
> > >
> > > Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> > > Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > > ---
> > > 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:

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