On 02/03/18 11:09, Wei Liu wrote: > On Thu, Mar 01, 2018 at 05:01:55PM +0000, Roger Pau Monné wrote: >> On Thu, Mar 01, 2018 at 04:01:23PM +0000, Wei Liu wrote: >>> 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 >> I've looked at the in-tree pvh document and it just refers to the local >> APIC in this sentence: >> >> "AP startup can be performed using hypercalls or the local APIC if present." >> >> I guess the trailing "if present" could be removed, but it's not >> colliding with this patch. >> >> I'm happy with rebasing this patch and applying the above change, is >> there any other document that should be changed? > Can we make it more explicit. Like > > VCPUs for PVH must have local APIC and it can't be disabled.
-1 to this. When an APIC is available to the guest, there is soft disable and hard disable as part of the state model. Saying this will only confuse the matter. ~Andrew _______________________________________________ Xen-devel mailing list Xenemail@example.com https://lists.xenproject.org/mailman/listinfo/xen-devel