Re: [XEN PATCH] x86/hvm: make ACPI PM timer support optional

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.09.2024 11:42, Sergiy Kibrik wrote:
> 23.09.24 13:01, Jan Beulich:
>>> --- a/xen/arch/x86/domain.c
>>> +++ b/xen/arch/x86/domain.c
>>> @@ -758,6 +758,9 @@ static bool emulation_flags_ok(const struct domain
>>> *d, uint32_t emflags)
>>>                 (X86_EMU_ALL & ~(X86_EMU_VPCI | X86_EMU_USE_PIRQ)) &&
>>>                 emflags != X86_EMU_LAPIC )
>>>                return false;
>>> +        if ( !is_hardware_domain(d) &&
>>> +             (emflags & X86_EMU_PM) && !IS_ENABLED(CONFIG_X86_PMTIMER))
>>> +            return false;
>>>        }
>>>        else if ( emflags != 0 && emflags != X86_EMU_PIT )
>>>        {
>> Why the is_hardware_domain() part of the check?
> 
> the idea was that since hardware domain has full hardware access it 
> probably doesn't need emulated timer. But this check will be dropped 
> anyway, as Roger suggested.
> 
>>
>>> (probably with X86_PMTIMER option depending on PV)
>> HVM you mean?
>>
> 
> I wanted to do it like this:
> 
> --- a/xen/arch/x86/Kconfig
> +++ b/xen/arch/x86/Kconfig
> @@ -386,7 +386,7 @@ config ALTP2M
>            If unsure, stay with defaults.
> 
>   config X86_PMTIMER
> -       bool "ACPI PM timer emulation support" if EXPERT
> +       bool "ACPI PM timer emulation support" if EXPERT && PV
>          default y
>          depends on HVM
>          help
> 
> to allow it to be disabled when PV is on and prevent situation when pvh 
> domain can't be created because !PV and hvm domain can't be created 
> either without emulated timer.

How does PV matter for this "depends on HVM" setting?

Jan