linux-kernel - Re: [PATCH v2] mshv: Extend create partition ioctl to support cpu features

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Message-ID: <28ab51c0-fe14-4122-8828-3f680207865d@linux.microsoft.com>
Date: Fri, 31 Oct 2025 13:08:45 -0700
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: Wei Liu <wei.liu@...nel.org>
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
 muislam@...rosoft.com, kys@...rosoft.com, haiyangz@...rosoft.com,
 decui@...rosoft.com, longli@...rosoft.com, mhklinux@...look.com,
 skinsburskii@...ux.microsoft.com, romank@...ux.microsoft.com,
 Jinank Jain <jinankjain@...rosoft.com>
Subject: Re: [PATCH v2] mshv: Extend create partition ioctl to support cpu
 features

On 10/31/2025 11:31 AM, Wei Liu wrote:
> On Thu, Oct 30, 2025 at 02:40:31PM -0700, Nuno Das Neves wrote:
>> From: Muminul Islam <muislam@...rosoft.com>
>>
>> The existing mshv create partition ioctl does not provide a way to
>> specify which cpu features are enabled in the guest. This was done
>> to reduce unnecessary complexity in the API.
>>
>> However, some new scenarios require fine-grained control over the
>> cpu feature bits.
>>
>> Define a new mshv_create_partition_v2 structure which supports passing
>> through the disabled cpu flags and xsave flags to the hypervisor
>> directly.
>>
>> When these are not specified (pt_num_cpu_fbanks == 0) or the old
>> structure is used, define a set of default flags which cover most
>> cases.
>>
>> Retain backward compatibility with the old structure via a new flag
>> MSHV_PT_BIT_CPU_AND_XSAVE_FEATURES which enables the new struct.
>>
>> Co-developed-by: Jinank Jain <jinankjain@...rosoft.com>
>> Signed-off-by: Jinank Jain <jinankjain@...rosoft.com>
>> Signed-off-by: Muminul Islam <muislam@...rosoft.com>
>> Signed-off-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
>> ---
>> Changes in v2:
>> - Fix compilation issues [kernel test robot]
>>
>> ---
>>  drivers/hv/mshv_root_main.c | 176 ++++++++++++++++++++++++++++++++----
>>  include/hyperv/hvhdk.h      |  86 +++++++++++++++++-
> 
> There is no mention of updating hvhdk.h in the commit message.
> 
Ah, that's true..

> Can you split out this part to a separate commit?

I put the header changes in this patch because a patch containing
those alone doesn't have much merit on its own.

I know we have split header changes into separate patches in the
past but I'm not sure it's always the right choice.

Thinking about this, I could also split it up another way: one
patch to introduce the new cpu features flags and use them in the
driver, and one patch to introduce mshv_create_partition_v2.

Nuno> 
> Wei