Re: [PATCH v2 2/5] apic: add support for x2APIC mode

[David Woodhouse]

On Wed, 2023-03-29 at 22:30 +0700, Bui Quang Minh wrote:
> 
> > 
> > I do some more testing on my hardware, your point is correct when dest 
> > == 0xffffffff, the interrupt is delivered to all APICs regardless of 
> > their mode.
> 
> To be precisely, it only broadcasts to CPUs in xAPIC mode if the IPI 
> destination mode is physical. In case the destination mode is logical, 
> flat model/cluster model rule applies to determine if the xAPIC CPUs 
> accept the IPI. Wow, this is so complicated :)

So even if you send to *all* of the first 8 CPUs in a cluster (e.g.
cluster 0x0001 giving a destination 0x000100FF, a CPU in xAPIC mode
doesn't see that as a broadcast because it's logical mode?

I would have assumed that a CPU in xAPIC mode would have looked at the
low byte and interpreted it as xAPIC logical mode, with the cluster in
the high nybble and the 4-bit mask in the low nybble?

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