Re: [PATCH] x86/MSI: fix guest unmasking when handling IRQ via event channel

[David Vrabel <david.vrabel@citrix.com>]

On 08/07/15 11:58, Jan Beulich wrote:
>>>> On 08.07.15 at 11:39, <david.vrabel@citrix.com> wrote:
>> On 08/07/15 09:56, Jan Beulich wrote:
>>> Rather than assuming only PV guests need special treatment (and
>>> dealing with that directly when an IRQ gets set up), keep all guest MSI
>>> IRQs masked until either the (HVM) guest unmasks them via vMSI or the
>>> (PV, PVHVM, or PVH) guest sets up an event channel for it.
>>>
>>> To not further clutter the common evtchn_bind_pirq() with x86-specific
>>> code, introduce an arch_evtchn_bind_pirq() hook instead.
>>
>> Can you describe the symptoms of the bug being fixed here?
> 
> Interrupts simply didn't get unmasked for PVHVM Linux guests.
> 
>>> --- a/xen/include/asm-arm/irq.h
>>> +++ b/xen/include/asm-arm/irq.h
>>> @@ -47,6 +47,8 @@ int release_guest_irq(struct domain *d, 
>>>  
>>>  void arch_move_irqs(struct vcpu *v);
>>>  
>>> +#define arch_evtchn_bind_pirq(d, pirq) ((void)((d) + (pirq)))
>>
>> Would this be better as a inline function?
>>
>>> +
>>>  /* Set IRQ type for an SPI */
>>>  int irq_set_spi_type(unsigned int spi, unsigned int type);
>>>  
>>> --- a/xen/include/xen/irq.h
>>> +++ b/xen/include/xen/irq.h
>>> @@ -172,4 +172,8 @@ unsigned int set_desc_affinity(struct ir
>>>  unsigned int arch_hwdom_irqs(domid_t);
>>>  #endif
>>>  
>>> +#ifndef arch_evtchn_bind_pirq
>>> +void arch_evtchn_bind_pirq(struct domain *, int pirq);
>>
>> ... moving this into xen/include/asm-x86/irq.h
> 
> Oh, right, (also to Julien) - this is exactly the reason I do not want it
> to be an inline function for ARM: I want the declaration here, not
> replicated in every interested arch's header.

Ok.

FWIW, with this requirement I would (instead of the macros) add a weak
arch_evtchn_bind_pirq() that's a no-op.

David