----- Original Message -----
> From: "Tom Lendacky" <[email protected]>
> To: "Paolo Bonzini" <[email protected]>, "Brijesh Singh"
> <[email protected]>, [email protected]
> Cc: [email protected], [email protected], [email protected],
> [email protected], [email protected],
> [email protected], [email protected], [email protected]
> Sent: Tuesday, November 22, 2016 3:25:52 PM
> Subject: Re: [PATCH v1 2/3] kvm: svm: Add kvm_fast_pio_in support
>
> On 11/21/2016 8:50 AM, Paolo Bonzini wrote:
> >
> >
> > On 14/11/2016 23:15, Brijesh Singh wrote:
> >> + /* For size less than 4 we merge, else we zero extend */
> >> + val = (size < 4) ? kvm_register_read(vcpu, VCPU_REGS_RAX) : 0;
> >
> > Are you sure it shouldn't always zero extend the high 32-bits? So "val"
> > should be declared as u32.
> >
> > Paolo
>
> It should only zero extend when dealing with a 32-bit operation. Any use
> of 8 or 16 bit registers leaves the upper 56 or 48 bits as is (see
> section 3.1.2.3 in http://support.amd.com/TechDocs/24592.pdf).
Duh, right, see also assign_register in arch/x86/kvm/emulate.c.
Paolo
> Thanks,
> Tom
>
> >
> >> + ret = emulator_pio_in_emulated(&vcpu->arch.emulate_ctxt, size, port,
> >> + &val, 1);
> >> + if (ret) {
> >> + kvm_register_write(vcpu, VCPU_REGS_RAX, val);
> >> + return ret;
> >> + }
>
