linux-kernel - Re: [PATCH 2/6] mshv: Ignore second stats page map result failure

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Message-ID: <efc78065-3556-410a-866f-961a7f1fc1ac@linux.microsoft.com>
Date: Fri, 5 Sep 2025 12:21:30 -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,
 easwar.hariharan@...ux.microsoft.com, kys@...rosoft.com,
 haiyangz@...rosoft.com, wei.liu@...nel.org, mhklinux@...look.com,
 decui@...rosoft.com, paekkaladevi@...ux.microsoft.com
Subject: Re: [PATCH 2/6] mshv: Ignore second stats page map result failure

On 8/28/2025 5:43 PM, Nuno Das Neves wrote:
> From: Purna Pavan Chandra Aekkaladevi <paekkaladevi@...ux.microsoft.com>
> 
> Some versions of the hypervisor do not support HV_STATUS_AREA_PARENT and
> return HV_STATUS_INVALID_PARAMETER for the second stats page mapping
> request.
> 
> This results a failure in module init. Instead of failing, gracefully
> fall back to populating stats_pages[HV_STATS_AREA_PARENT] with the
> already-mapped stats_pages[HV_STATS_AREA_SELF].

What's the impact of this graceful fallback? It occurs to me that if a stats
accumulator, in userspace perhaps, expected to get stats from the 2 pages,
it'd get incorrect values.

> 
> Signed-off-by: Purna Pavan Chandra Aekkaladevi <paekkaladevi@...ux.microsoft.com>
> Signed-off-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
> ---
>  drivers/hv/mshv_root_hv_call.c | 43 ++++++++++++++++++++++++++++++----
>  drivers/hv/mshv_root_main.c    |  3 +++
>  2 files changed, 42 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hv/mshv_root_hv_call.c b/drivers/hv/mshv_root_hv_call.c
> index c9c274f29c3c..1c38576a673c 100644
> --- a/drivers/hv/mshv_root_hv_call.c
> +++ b/drivers/hv/mshv_root_hv_call.c
> @@ -724,6 +724,24 @@ hv_call_notify_port_ring_empty(u32 sint_index)
>  	return hv_result_to_errno(status);
>  }
>  
> +static int
> +hv_stats_get_area_type(enum hv_stats_object_type type,

One line please, i.e.

static int hv_stats_get_area_type(...)

<snip>

Thanks,
Easwar (he/him)