Re: [Xen-devel] [PATCH xen v2] xen: arm: fully implement multicall interface.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.04.14 at 17:18, <Ian.Campbell@xxxxxxxxxx> wrote:
> On Mon, 2014-04-07 at 16:13 +0100, Jan Beulich wrote:
>> >> On x86 we actually decided quite a long while ago to try to avoid
>> >> domain_crash_synchronous() whenever possible.
> 
> I meant to ask why this was?
> 
> I'm supposing that the for(;;) do_softirqs is not considered very
> nice...

That plus it misguides you into not writing proper error path code.

>> You'd want to return some error indication, avoid anything else to be
>> done that might confusion on a dead domain (read: abort the entire
>> multicall),
> 
> Hrm, that will involve frobbing around with the common do_multicall code
> since it currently doesn't consider the possibility of do_multicall_call
> failing in a fatal way.

But then again - is there anything wrong with actually carrying
out the multicall (with truncated arguments), resulting in the
domain dying only slightly later?

>>  and on the hypercall exit path the vCPU would be taken off
>> the scheduler, i.e. you run your normal call tree to completion and
>> you're guaranteed that the vCPU in question won't make it back into
>> guest context.
> 
> What about other vcpus? I suppose they get nobbled as and when they
> happen to enter the hypervisor?

Sure - via domain_shutdown() they all get vcpu_pause_nosync()'ed,
i.e. they're being forced into the hypervisor if not already there.

Jan


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