From: Paul Durrant <Paul.Durrant@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Wei Liu <wei.liu2@citrix.com>,
Andrew Cooper <Andrew.Cooper3@citrix.com>,
Stefano Stabellini <Stefano.Stabellini@citrix.com>,
Ian Jackson <Ian.Jackson@citrix.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
"Keir (Xen.org)" <keir@xen.org>
Subject: Re: [PATCH 2/2] x86/hvm/viridian: Enable APIC assist enlightenment
Date: Wed, 16 Mar 2016 17:23:26 +0000 [thread overview]
Message-ID: <9778e6d31c454e09adda577a595b2bdf@AMSPEX02CL03.citrite.net> (raw)
In-Reply-To: <56E997A702000078000DD4BC@prv-mh.provo.novell.com>
> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@suse.com]
> Sent: 16 March 2016 16:28
> To: Paul Durrant
> Cc: Andrew Cooper; Ian Jackson; Stefano Stabellini; Wei Liu; xen-
> devel@lists.xenproject.org; Konrad Rzeszutek Wilk; Keir (Xen.org)
> Subject: RE: [Xen-devel] [PATCH 2/2] x86/hvm/viridian: Enable APIC assist
> enlightenment
>
> >>> On 16.03.16 at 16:02, <Paul.Durrant@citrix.com> wrote:
> >> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@oracle.com]
> >> Sent: 15 March 2016 23:18
> >> On Tue, Mar 15, 2016 at 04:14:16PM +0000, Paul Durrant wrote:
> >> > + domain_crash(v->domain);
> >> > +
> >> > + v->arch.hvm_vcpu.viridian.apic_assist.vector = vector;
> >> > + *(uint32_t *)va |= 1u;
> >>
> >> Oh my. What does that do? Why not 0xBADF00D
> >> Is that prescriped in the spec?
> >
> > The LSB is the only bit that has defined functionality. The next 31 bits are
> > reserved and the rest of the page is undefined.
> >
> >>
> >> That looks quite unhealthy to do.
> >>
> >
> > Reading the spec. again I do see that the reserved bits are defined to be
> > zero, so it looks like I can use = rather than |=.
>
> Wouldn't that put at risk forward compatibility?
>
The spec just says "Reserved to Zero" so it's hard to know what the right thing to do is until further bits are defined.
Paul
> Jan
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next prev parent reply other threads:[~2016-03-16 18:10 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-15 16:14 [PATCH 0/2] x86/hvm/viridian: APIC assist Paul Durrant
2016-03-15 16:14 ` [PATCH 1/2] x86/hvm/viridian: keep APIC assist page mapped Paul Durrant
2016-03-15 23:20 ` Konrad Rzeszutek Wilk
2016-03-16 14:46 ` Paul Durrant
2016-03-15 16:14 ` [PATCH 2/2] x86/hvm/viridian: Enable APIC assist enlightenment Paul Durrant
2016-03-15 23:18 ` Konrad Rzeszutek Wilk
2016-03-16 15:02 ` Paul Durrant
2016-03-16 16:28 ` Jan Beulich
2016-03-16 17:23 ` Paul Durrant [this message]
2016-03-17 8:12 ` Jan Beulich
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