[Xen-devel] Re: [PATCH 1/2] x86, hvm: allow another vcpu to receive PIT IRQ (support kexec/kdump on hvm)

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 30/06/2009 08:57, "Kouya Shimura" <kouya@xxxxxxxxxxxxxx> wrote:

>> Really? Why would it do that?
> 
> Not always. kdump leaves one cpu which has received a crash signal
> and halts all other cpus. I don't know why.

That seems very brave of it, if it also expects interrupts to still work!
Does it really require *all* interrupts still to be functional?

>> These patches are pretty nasty. We can perhaps come up with a neater smaller
>> version of them if there's a real need.
> 
> Hmm, though I tried to make them small...
> Could you refine them?

Well, looking at patch 1/2 to start with, some of the issues you address are
not particular to the PIT, but to any interrupt delivered via vpt.c. I
suspect what you really need is a hook into vpt.c when a vcpu goes down, to
move all its vpt's (except its own LAPIC one) onto another vcpu's list. And
on create_periodic_time() ignore the suggested vcpu given by the caller if
that vcpu is down. And disable the IRQ0_SPECIAL_ROUTING in vioapic.c if
vcpu0 is down.

Patch 2/2 I suppose something like that might be acceptable. Still it'd be
nice to not have every VCPU piling into hvm_dirq_assist(). Perhaps that and
vpt.c could agree on who their current 'fallback vcpu' is, and have that
inherit orphaned vpts and do all dirq assistance.

It's still a bit fragile and a bit of a pain in the butt though. Is kdump in
HVM guests super important?

 -- Keir



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