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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
