Re: [PATCH 2/2] x86/pvh: also print hardware domain pIRQ limit for PVH

[Jan Beulich <jbeulich@xxxxxxxx>]

On 21.11.2024 12:24, Roger Pau Monné wrote:
> On Thu, Nov 21, 2024 at 11:14:23AM +0000, Andrew Cooper wrote:
>> On 21/11/2024 11:08 am, Roger Pau Monné wrote:
>>> On Thu, Nov 21, 2024 at 11:54:49AM +0100, Jan Beulich wrote:
>>>> On 20.11.2024 12:35, Roger Pau Monne wrote:
>>>>> Do not return early in the PVH/HVM case, so that the number of pIRQs is 
>>>>> also
>>>>> printed.
>>>> What you're printing ...
>>>>
>>>>> Fixes: 17f6d398f765 ('cmdline: document and enforce "extra_guest_irqs" 
>>>>> upper bounds')
>>>>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>>>> ---
>>>>>  xen/arch/x86/io_apic.c | 12 +++++++-----
>>>>>  1 file changed, 7 insertions(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/xen/arch/x86/io_apic.c b/xen/arch/x86/io_apic.c
>>>>> index bd5ad61c85e4..d9db2efc4f58 100644
>>>>> --- a/xen/arch/x86/io_apic.c
>>>>> +++ b/xen/arch/x86/io_apic.c
>>>>> @@ -2754,11 +2754,13 @@ unsigned int __hwdom_init arch_hwdom_irqs(const 
>>>>> struct domain *d)
>>>>>  
>>>>>      /* PVH (generally: HVM) can't use PHYSDEVOP_pirq_eoi_gmfn_v{1,2}. */
>>>>>      if ( is_hvm_domain(d) )
>>>>> -        return nr_irqs;
>>>>> -
>>>>> -    if ( !d->domain_id )
>>>>> -        n = min(n, dom0_max_vcpus());
>>>>> -    n = min(nr_irqs_gsi + n * NR_DYNAMIC_VECTORS, max_irqs);
>>>>> +        n = nr_irqs;
>>>> ... is rather the number of IRQs we picked for the system. That may happen 
>>>> to
>>>> end up being the upper bound for PVH Dom0, yet not logging this at all was
>>>> because of the limited use pIRQ-s have there. Granted at the time I was 
>>>> still
>>>> under the impression they have no use there at all, so this isn't really an
>>>> objection to the change. I would have been nice though if the description 
>>>> had
>>>> mentioned why significance pIRQ-s actually have in PVH Dom0.
>>> Sure, what about adding to the commit message:
>>>
>>> "While PVH dom0 doesn't have access to the hypercalls to manage pIRQs
>>> itself, neither the knowledge to do so, pIRQs are still used by Xen to
>>> map and bind interrupts to a PVH dom0 behind its back.  Hence the
>>> pIRQ limit is still relevant for a PVH dom0."
>>
>> Minor grammar point.  You want "nor" rather than "neither" in this
>> context, because it's introducing the second of two negative things.
> 
> Thanks!  Could one of you adjust at commit if Jan agrees with adding
> the paragraph?

Sounds good, and certainly not a problem to add while committing.

Jan