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

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Message-ID: <8520ef42-6cb4-4e14-9700-de7ae8a99ae8@linux.microsoft.com>
Date: Wed, 12 Mar 2025 11:04:37 -0700
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: Michael Kelley <mhklinux@...look.com>,
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Subject: Re: [PATCH v5 02/10] x86/mshyperv: Add support for extended Hyper-V
 features

On 3/6/2025 10:30 AM, Michael Kelley wrote:
> From: Nuno Das Neves <nunodasneves@...ux.microsoft.com> Sent: Wednesday, February 26, 2025 3:08 PM
>>
>> From: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
>>
>> 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@...ux.microsoft.com>
>> Signed-off-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
>> ---
>>  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.

Just checked - yes ARM64 has features in ECX, but they are different to the x86_64 ones.
We can add the ARM64 ones when needed.

Thanks
Nuno

> 
> 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@...look.com>