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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

~Andrew