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

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Message-ID: <119f11e7-6074-4bd4-a72b-fc76370c284f@linux.microsoft.com>
Date: Fri, 31 Oct 2025 11:37:40 -0700
From: Easwar Hariharan <easwar.hariharan@...ux.microsoft.com>
To: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
 muislam@...rosoft.com, easwar.hariharan@...ux.microsoft.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 10/30/2025 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,
Easwar (he/him)

<snip>