lkml.org 
[lkml]   [2016]   [Nov]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v1 2/3] kvm: svm: Add kvm_fast_pio_in support


----- Original Message -----
> From: "Tom Lendacky" <thomas.lendacky@amd.com>
> To: "Paolo Bonzini" <pbonzini@redhat.com>, "Brijesh Singh" <brijesh.singh@amd.com>, kvm@vger.kernel.org
> Cc: rkrcmar@redhat.com, joro@8bytes.org, x86@kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com,
> hpa@zytor.com, tglx@linutronix.de, bp@suse.de
> 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;
> >> + }
>

\
 
 \ /
  Last update: 2016-11-22 16:13    [W:0.046 / U:0.236 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site