Re: [PATCH] KVM: x86: amend APIC lowest priority arbitration

["Radim Krčmář" <rkrcmar@redhat.com>]

2015-01-09 15:37+0100, Radim Krčmář:
> Lowest priority should take the task priority into account.
> 
> SDM 10.6.2.4 Lowest Priority Delivery Mode.
> (Too long to quote; second and last paragraphs are relevant.)
> 
> Before this patch, we strived to have the same amount of handled
> lowest-priority interrupts on all VCPUs.
> This is only a complication, but kept for compatibility.

> Real modern Intels can't send lowest priority IPIs and the chipset
> directs external ones using processors' TPR.

False, new Intels most likely don't consider TPR.
Please don't include this patch.

> AMD still has rough edges.

AMD behaves like its documentation states,

> +	/* XXX: AMD (2:16.6.2 Lowest Priority Messages and Arbitration)
> +	 *      - uses the APR register (which also considers ISR and IRR),
> +	 *      - chooses the highest APIC ID when APRs are identical,
> +	 *      - and allows a focus processor.

but we don't differentiate.  (It shouldn't create AMD-specific bugs.)