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Re: [XEN PATCH v1 1/3] x86/hvm: introduce config option for ACPI PM timer


  • To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Fri, 4 Oct 2024 15:30:34 +0200
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  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>
  • Delivery-date: Fri, 04 Oct 2024 13:30:54 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 04.10.2024 15:09, Roger Pau Monné wrote:
> On Fri, Oct 04, 2024 at 12:31:50PM +0300, Sergiy Kibrik wrote:
>> --- a/xen/arch/x86/include/asm/domain.h
>> +++ b/xen/arch/x86/include/asm/domain.h
>> @@ -496,7 +496,8 @@ struct arch_domain
>>  
>>  #define has_vlapic(d)      (!!((d)->arch.emulation_flags & X86_EMU_LAPIC))
>>  #define has_vhpet(d)       (!!((d)->arch.emulation_flags & X86_EMU_HPET))
>> -#define has_vpm(d)         (!!((d)->arch.emulation_flags & X86_EMU_PM))
>> +#define has_vpm(d)         (IS_ENABLED(CONFIG_X86_PMTIMER) && \
>> +                            !!((d)->arch.emulation_flags & X86_EMU_PM))
> 
> Do you really need the IS_ENABLED() here?  If you modify
> emulation_flags_ok() to reject the flag if not available it won't be
> possible for any domain to have it set.

With the IS_ENABLED() the only other approach to have the compiler DCE any
code left unreachable would be to #define X86_EMU_PM to 0 in that case. I
guess I'd slightly prefer that alternative, but otherwise the approach used
here would still be wanted imo.

Jan



 


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