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Re: [Xen-devel] [PATCH v3 03/13] xen: introduce cpumask_from_bitmap

On Thu, 2013-04-25 at 15:26 +0100, Keir Fraser wrote:
> On 25/04/2013 11:01, "Ian Campbell" <Ian.Campbell@xxxxxxxxxx> wrote:
> >> And most importantly: Why? This isn't an operation that should
> >> commonly be done, and hence having a utility function for this
> >> seems to invite for abuse rather than really help.
> > 
> > I suggested it, we are emulating an instruction which provides a bitmap
> > of the CPUs to operate on. It seemed nicer to me to have a helper rather
> > than to open-code accesses under the hood of the cpumask interface.
> Emulating a guest instruction? And it really wants to act on sets of real
> physical cpus (hence cpumask_t)?

It's emulating a write to a GICD (read: APIC ;-)) register which causes
an SGI (read: IPI) to be sent. The value you write includes an 8 bit
mask indicating the target processors.

See "[PATCH v3 04/13] xen/arm: support for guest SGI" in this series.


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