Re: [PATCH] enable x2APIC without interrupt remapping under KVM

Ingo Molnar
2009-07-10T13:56:33Z

* Gleb Natapov <gleb@redhat.com> wrote:

> KVM would like to provide x2APIC interface to a guest without emulating
> interrupt remapping device. The reason KVM prefers guest to use x2APIC
> is that x2APIC interface is better virtualizable and provides better
> performance than mmio xAPIC interface:
>
> - msr exits are faster than mmio (no page table walk, emulation)
> - no need to read back ICR to look at the busy bit
> - one 64 bit ICR write instead of two 32 bit writes
> - shared code with the Hyper-V paravirt interface
>
> Included patch changes x2APIC enabling logic to enable it even if IR
> initialization failed, but kernel runs under KVM and no apic id is
> greater than 255 (if there is one spec requires BIOS to move to x2apic
> mode before starting an OS).
>
> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>
> ---
>
> This is the same as v5 only rebased on x86 tree (a74d2cea).

Looks good.

Small detail: please run the patch through scripts/checkpatch.pl and
fix the complaints it has - all 3 details it points out seem like
valid complaints to me (at a quick glance) that should be fixed.

Thanks,

Ingo