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

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Message-ID: <ae9c0915-3472-4929-9bfa-866171d32758@linux.microsoft.com>
Date: Fri, 31 Oct 2025 12:49:12 -0700
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: Easwar Hariharan <easwar.hariharan@...ux.microsoft.com>
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
 muislam@...rosoft.com, kys@...rosoft.com, haiyangz@...rosoft.com,
 wei.liu@...nel.org, 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 11:37 AM, Easwar Hariharan wrote:
> On 10/30/2025 2:40 PM, 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 +++++++++++++++++-
>>  include/uapi/linux/mshv.h   |  34 +++++++
>>  3 files changed, 272 insertions(+), 24 deletions(-)
> 
> lkp also pointed out that we are leaking a kernel config to userspace:
> https://lore.kernel.org/all/202510292330.LCHvPCLt-lkp@intel.com/
> 
> In the v3 that Wei requested, please address that as well.

Thanks, I did fix this issue in v2 but I didn't mention it explicitly.
I'll update the changelog in v3 to call it out.

> 
> Thanks,
> Easwar (he/him)
> 
> <snip>