Re: [Xen-devel] [PATCH] x86/vlapic: Don't reset APIC mode/ID when handling INIT signal

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 04/19/2017 09:21 AM, Jan Beulich wrote:
> > > > On 19.04.17 at 06:56, <chao.gao@xxxxxxxxx> wrote:
> > On Wed, Apr 19, 2017 at 02:48:57AM -0600, Jan Beulich wrote:
> > > > > > On 18.04.17 at 23:51, <chao.gao@xxxxxxxxx> wrote:
> > > > HVM guest can't enable x2apic as XENFEAT_hvm_pirqs is exposed to it.
> > > > Why we have this restriction? As a consequence, This patch isn't
> > > > tested in that case.
> > > HVM guests very well can use x2APIC, I'm seeing them use it all
> > > the time. Please be more specific with your question.
> > OK. I failed to enable guest's x2apic, with the output: IRQ Remapping doesn't
> > support X2APIC mode. Eventually, I found the xen_x2apic_para_available()
> > in linux kernel and it returns false when Xen exposes XENFEAT_hvm_pirqs to
> > guest.
> Looks more like a Linux/pvops question, which I continue to not
> really be an expert on. Let's ask the maintainers (now Cc-ed)
> (but it may well be that this simply depends on whether you
> enable PVHVM mode)...
Interestingly enough, I was looking at this last week and wondering why 
it was there. Ankur (copied) found an issue related to x2apic he thought 
was PVH-specific, but that was because HVM guests don't turn it on.
Konrad couldn't remember why it was there neither.

-boris

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