Re: [PATCH v5 04/10] hyperv: Introduce hv_recommend_using_aeoi()

[Nuno Das Neves <nunodasneves@linux.microsoft.com>]

On 2/27/2025 3:03 PM, Easwar Hariharan wrote:
> On 2/26/2025 3:07 PM, Nuno Das Neves wrote:
>> Factor out the check for enabling auto eoi, to be reused in root
>> partition code.
>>
>> Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
>> ---
>>  drivers/hv/hv.c                | 12 +-----------
>>  include/asm-generic/mshyperv.h | 13 +++++++++++++
>>  2 files changed, 14 insertions(+), 11 deletions(-)
>>
> 
> <snip>
> 
>> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
>> index 258034dfd829..1f46d19a16aa 100644
>> --- a/include/asm-generic/mshyperv.h
>> +++ b/include/asm-generic/mshyperv.h
>> @@ -77,6 +77,19 @@ extern u64 hv_do_fast_hypercall16(u16 control, u64 input1, u64 input2);
>>  bool hv_isolation_type_snp(void);
>>  bool hv_isolation_type_tdx(void);
>>  
>> +/*
>> + * On architectures where Hyper-V doesn't support AEOI (e.g., ARM64),
>> + * it doesn't provide a recommendation flag and AEOI must be disabled.
>> + */
>> +static inline bool hv_recommend_using_aeoi(void)
>> +{
>> +#ifdef HV_DEPRECATING_AEOI_RECOMMENDED
>> +	return !(ms_hyperv.hints & HV_DEPRECATING_AEOI_RECOMMENDED);
>> +#else
>> +	return false;
>> +#endif
>> +}
>> +
> 
> I must be missing something very basic here, and if so, I apologize, and please enlighten me.
> 
> HV_DEPRECATING_AEOI_RECOMMENDED is defined as BIT(9) in include/hyperv/hvgdk_mini.h, and
> asm-generic/mshyperv.h includes that via include/hyperv/hvhdk.h.
> 
> If this is the case, when would HV_DEPRECATING_AEOI_RECOMMENDED ever be not defined?
> If it's always defined, do we need the #ifdef?
> 
HV_DEPRECATING_AEOI_RECOMMENDED is only defined on x86 (it used to live in x86 hyperv-tlfs.h).
It lives inside a #if defined(CONFIG_X86) block in hvgdk_mini.h. It is a bit confusing since
it is surrounded by other x86-only definitions which are prefixed with HV_X64_.

Thanks
Nuno

> Thanks,
> Easwar (he/him)