[PATCH v2 9/9] arm64: KVM: vgic: deal with GIC sub-page alignment

Peter Maydell peter.maydell at linaro.org
Tue Jun 24 15:28:28 PDT 2014

On 24 June 2014 20:28, Joel Schopp <joel.schopp at amd.com> wrote:
> On 06/19/2014 04:21 AM, Marc Zyngier wrote:
>> The GIC CPU interface is always 4k aligned. If the host is using
>> 64k pages, it is critical to place the guest's GICC interface at the
>> same relative alignment as the host's GICV. Failure to do so results
>> in an impossibility for the guest to deal with interrupts.
>> Add a KVM_DEV_ARM_VGIC_GRP_ADDR_OFFSET attribute for the VGIC, allowing
>> userspace to retrieve the GICV offset in a page. It becomes then trivial
>> to adjust the GICC base address for the guest.
> Does this mean there is a corresponding patch for qemu?

Not as far as I know. It's a bit awkward on the QEMU end because
we really want to provide the guest a consistent memory map
regardless of the host CPU. So at best we'd probably use it to
say "sorry, can't run on this CPU/host kernel".

(That said, if you think you can make QEMU usefully use the
information and want to write a QEMU patch I'm not averse
to the idea.)

kvmtool is probably better placed to take advantage of it since
it takes more of a "deal with what the host provides you"

-- PMM

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