Re: [PATCH v2] xen/pci: Refactor PCI MSI interrupts related code

[Jan Beulich <jbeulich@suse.com>]

On 13.04.2021 19:12, Julien Grall wrote:
> On 12/04/2021 11:49, Roger Pau Monné wrote:
>> On Fri, Apr 09, 2021 at 05:00:41PM +0100, Rahul Singh wrote:
>>> --- a/xen/include/xen/vpci.h
>>> +++ b/xen/include/xen/vpci.h
>>> @@ -91,6 +91,7 @@ struct vpci {
>>>           /* FIXME: currently there's no support for SR-IOV. */
>>>       } header;
>>>   
>>> +#ifdef CONFIG_PCI_MSI_INTERCEPT
>>>       /* MSI data. */
>>>       struct vpci_msi {
>>>         /* Address. */
>>> @@ -136,6 +137,7 @@ struct vpci {
>>>               struct vpci_arch_msix_entry arch;
>>>           } entries[];
>>>       } *msix;
>>> +#endif /* CONFIG_PCI_MSI_INTERCEPT */
>>
>> Note that here you just remove two pointers from the struct, not that
>> I'm opposed to it, but it's not that much space that's saved anyway.
>> Ie: it might also be fine to just leave them as NULL unconditionally
>> on Arm.
> 
> Can the two pointers be NULL on x86? If not, then I would prefer if they 
> disappear on Arm so there is less chance to make any mistake (such as 
> unconditionally accessing the pointer in common code).

Alternative proposal: How about making it effectively impossible to
de-reference the pointer on Arm by leaving the field there, but having
the struct definition available on non-Arm only?

Jan