RE: [PATCH v5 02/10] x86/mshyperv: Add support for extended Hyper-V features

[Michael Kelley]

From: Nuno Das Neves <nunodasneves@xxxxxxxxxxxxxxxxxxx> Sent: Wednesday, February 26, 2025 3:08 PM
> 
> From: Stanislav Kinsburskii <skinsburskii@xxxxxxxxxxxxxxxxxxx>
> 
> Extend the "ms_hyperv_info" structure to include a new field,
> "ext_features", for capturing extended Hyper-V features.
> Update the "ms_hyperv_init_platform" function to retrieve these features
> using the cpuid instruction and include them in the informational output.
> 
> Signed-off-by: Stanislav Kinsburskii <skinsburskii@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Nuno Das Neves <nunodasneves@xxxxxxxxxxxxxxxxxxx>
> ---
>  arch/x86/kernel/cpu/mshyperv.c | 6 ++++--
>  include/asm-generic/mshyperv.h | 1 +
>  2 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 4f01f424ea5b..2c29dfd6de19 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -434,13 +434,15 @@ static void __init ms_hyperv_init_platform(void)
>  	 */
>  	ms_hyperv.features = cpuid_eax(HYPERV_CPUID_FEATURES);
>  	ms_hyperv.priv_high = cpuid_ebx(HYPERV_CPUID_FEATURES);
> +	ms_hyperv.ext_features = cpuid_ecx(HYPERV_CPUID_FEATURES);
>  	ms_hyperv.misc_features = cpuid_edx(HYPERV_CPUID_FEATURES);
>  	ms_hyperv.hints    = cpuid_eax(HYPERV_CPUID_ENLIGHTMENT_INFO);
> 
>  	hv_max_functions_eax = cpuid_eax(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS);
> 
> -	pr_info("Hyper-V: privilege flags low 0x%x, high 0x%x, hints 0x%x, misc 0x%x\n",
> -		ms_hyperv.features, ms_hyperv.priv_high, ms_hyperv.hints,
> +	pr_info("Hyper-V: privilege flags low 0x%x, high 0x%x, ext 0x%x, hints 0x%x, misc 0x%x\n",
> +		ms_hyperv.features, ms_hyperv.priv_high,
> +		ms_hyperv.ext_features, ms_hyperv.hints,
>  		ms_hyperv.misc_features);
> 
>  	ms_hyperv.max_vp_index = cpuid_eax(HYPERV_CPUID_IMPLEMENT_LIMITS);
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index dc4729dba9ef..c020d5d0ec2a 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -36,6 +36,7 @@ enum hv_partition_type {
>  struct ms_hyperv_info {
>  	u32 features;
>  	u32 priv_high;
> +	u32 ext_features;
>  	u32 misc_features;
>  	u32 hints;
>  	u32 nested_features;
> --
> 2.34.1

Are any of the extended features available on arm64? This code is obviously x86 specific,
so ms_hyperv.ext_features will be zero on arm64. From what I can see, ext_features is
referenced only in Patch 10 of this series, and in code that is under #ifdef CONFIG_X86_64,
so that should be OK.

The pr_info() line will now be slightly different on x86 and arm64 since arm64 won't have
the "ext" field, but I think that's OK too.

Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>