linux-kernel - Re: [PATCH v5 04/10] hyperv: Introduce hv_recommend_using

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Message-ID: <57426824-5302-4200-8560-8eb67be6b378@linux.microsoft.com>
Date: Thu, 27 Feb 2025 16:49:48 -0800
From: Easwar Hariharan <eahariha@...ux.microsoft.com>
To: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
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Subject: Re: [PATCH v5 04/10] hyperv: Introduce hv_recommend_using_aeoi()

On 2/27/2025 4:33 PM, Nuno Das Neves wrote:
> 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@...ux.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_.
> 

Ah, thank you. I knew it must be something glaringly obvious in hindsight. With that resolved,

Reviewed-by: Easwar Hariharan <eahariha@...ux.microsoft.com>