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

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Message-ID: <7749367d-d87d-43f0-8c24-cd08bb4ce1a8@linux.microsoft.com>
Date: Thu, 27 Feb 2025 15:03:22 -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 2/26/2025 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?

Thanks,
Easwar (he/him)