Messages in this thread | | | Subject | Re: [Xen-devel] [PATCH 8/8] xen/pvh: Enable CPU hotplug | From | Andrew Cooper <> | Date | Thu, 27 Oct 2016 16:00:26 +0100 |
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On 27/10/16 15:25, Boris Ostrovsky wrote: > > > On 10/14/2016 03:01 PM, Boris Ostrovsky wrote: >> On 10/14/2016 02:41 PM, Andrew Cooper wrote: >>> On 14/10/16 19:05, Boris Ostrovsky wrote: >>>> PVH guests don't receive ACPI hotplug interrupts and therefore >>>> need to monitor xenstore for CPU hotplug event. >>> Why not? If they don't, they should. As we are providing ACPI anyway, >>> we should provide all bits of it. >> >> We don't have IOAPIC, which is how these interrupts are typically >> delivered. I suppose we might be able to specify it as something else. >> >> I'll look into this. > > > (+Jan) > > Yes, we can do this. The main issue is how to deal with event > registers (i.e FADT.x_pm1a_evt_blk) and AML's PRST region (which > specifies online CPU map). > > Currently these are accessed via IO space and are handled by qemu. > > There are a couple of ways to deal with this that I can see. > > 1. We can implement ioreq handling in the hypervisor, there are only a > few addresses that need handling. > > 2. We can implement those registers in memory space and have libxl > update them them on a hotplug command. This appears to be possible > because these registers mostly just consume writes without side > effects so they can be simple memory locations. The one exception is > updating status bits (they are cleared by writing 1s) but I think we > can do this from the AML. > > Other than that the only other thing is setting up an event channel > between the toolstack and the guest (either via xenstore or perhaps by > having a reserved port for SCI). > > I have a prototype with (2) (except for the bit clearing part) but I > want to hear comments on this approach before I write proper patches.
Xen already deals with 1 for HVM guests. We should do the same for PVH guests as well.
-1 to anything involving looping a PVH dom0 back around to some entity running inside dom0.
~Andrew
~Andrew
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