Re: [Xen-devel] [PATCH] xl: remove apic option for PVH guests

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Mar 01, 2018 at 03:57:18PM +0000, Andrew Cooper wrote:
> On 01/03/18 12:22, Wei Liu wrote:
> > On Wed, Feb 28, 2018 at 10:20:53AM +0000, Roger Pau Monne wrote:
> >> XSA-256 forces the local APIC to always be enabled for PVH guests, so
> >> ignore any apic option for PVH guests. Update the documentation
> >> accordingly.
> > I think how I will approach this is to dictate that PVH always has LAPIC
> > in our in-tree document, then use that as the justification for this
> > change. That's the consensus from 2 years ago, right?
> >
> > Or we're just working around the limitation in our code base, and users
> > may demand a no-LAPIC PVH guest just because...
> 
> Currently, Xen enforces that HVM guests have an LAPIC.  This is because
> making the non-LAPIC case function correctly/safely devolved into a
> massive rats nest and I stopped trying to fix it after 2 days of trying.
> 
> At the moment, it would be wise to discuss whether the non-LAPIC case is
> actually sensible.  I personally see no value in keeping it.
> 

+1

> If someone can come up with a convincing usecase for keeping it, then
> ok, but the barrier for this is increasing all the time, especially now
> that hardware acceleration and posted interrupts means that a
> pipeline-virtualised APIC is faster and more efficient than any of our
> event channel mechanisms.

+1

Wei.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel