Messages in this thread | | | Date | Tue, 14 Jul 2015 16:04:24 -0400 | From | Boris Ostrovsky <> | Subject | Re: [Xen-devel] [patch 1/4] hotplug: Prevent alloc/free of irq descriptors during cpu up/down |
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On 07/14/2015 01:32 PM, Thomas Gleixner wrote: > On Tue, 14 Jul 2015, Boris Ostrovsky wrote: >> On 07/14/2015 11:44 AM, Thomas Gleixner wrote: >>> On Tue, 14 Jul 2015, Boris Ostrovsky wrote: >>>>> Prevent allocation and freeing of interrupt descriptors accross cpu >>>>> hotplug. >>>> This breaks Xen guests that allocate interrupt descriptors in .cpu_up(). >>> And where exactly does XEN allocate those descriptors? >> xen_cpu_up() >> xen_setup_timer() >> bind_virq_to_irqhandler() >> bind_virq_to_irq() >> xen_allocate_irq_dynamic() >> xen_allocate_irqs_dynamic() >> irq_alloc_descs() >> >> >> There is also a similar pass via xen_cpu_up() -> xen_smp_intr_init() > Sigh. > >>> >>>> Any chance this locking can be moved into arch code? >>> No. > The issue here is that all architectures need that protection and just > Xen does irq allocations in cpu_up. > > So moving that protection into architecture code is not really an > option. > >>>> Otherwise we will need to have something like arch_post_cpu_up() >>>> after the lock is released. > I'm not sure, that this will work. You probably want to do this in the > cpu prepare stage, i.e. before calling __cpu_up().
For PV guests (the ones that use xen_cpu_up()) it will work either before or after __cpu_up(). At least my (somewhat limited) testing didn't show any problems so far.
However, HVM CPUs use xen_hvm_cpu_up() and if you read comments there you will see that xen_smp_intr_init() needs to be called before native_cpu_up() but xen_init_lock_cpu() (which eventually calls irq_alloc_descs()) needs to be called after.
I think I can split xen_init_lock_cpu() so that the part that needs to be called after will avoid going into irq core code. And then the rest will go into arch_cpu_prepare().
-boris
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