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

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Message-ID: <CAMvTesA17jtxN_L3QbbVGUcjnPRYtNZWHzFmCYgqZosOrM0RoQ@mail.gmail.com>
Date: Sun, 7 Sep 2025 01:30:56 +0800
From: Tianyu Lan <ltykernel@...il.com>
To: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org, 
	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 Fri, Aug 29, 2025 at 8:44 AM Nuno Das Neves
<nunodasneves@...ux.microsoft.com> 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].
>
> 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(-)
>
Reviewed-by: Tianyu Lan <tiala@...rosoft.com>

> 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,
> +                      const union hv_stats_object_identity *identity)
> +{
> +       switch (type) {
> +       case HV_STATS_OBJECT_HYPERVISOR:
> +               return identity->hv.stats_area_type;
> +       case HV_STATS_OBJECT_LOGICAL_PROCESSOR:
> +               return identity->lp.stats_area_type;
> +       case HV_STATS_OBJECT_PARTITION:
> +               return identity->partition.stats_area_type;
> +       case HV_STATS_OBJECT_VP:
> +               return identity->vp.stats_area_type;
> +       }
> +
> +       return -EINVAL;
> +}
> +
>  int hv_call_map_stat_page(enum hv_stats_object_type type,
>                           const union hv_stats_object_identity *identity,
>                           void **addr)
> @@ -732,7 +750,7 @@ int hv_call_map_stat_page(enum hv_stats_object_type type,
>         struct hv_input_map_stats_page *input;
>         struct hv_output_map_stats_page *output;
>         u64 status, pfn;
> -       int ret = 0;
> +       int hv_status, ret = 0;
>
>         do {
>                 local_irq_save(flags);
> @@ -747,11 +765,28 @@ int hv_call_map_stat_page(enum hv_stats_object_type type,
>                 pfn = output->map_location;
>
>                 local_irq_restore(flags);
> -               if (hv_result(status) != HV_STATUS_INSUFFICIENT_MEMORY) {
> -                       ret = hv_result_to_errno(status);
> +
> +               hv_status = hv_result(status);
> +               if (hv_status != HV_STATUS_INSUFFICIENT_MEMORY) {
>                         if (hv_result_success(status))
>                                 break;
> -                       return ret;
> +
> +                       /*
> +                        * Some versions of the hypervisor do not support the
> +                        * PARENT stats area. In this case return "success" but
> +                        * set the page to NULL. The caller checks for this
> +                        * case instead just uses the SELF area.
> +                        */
> +                       if (hv_stats_get_area_type(type, identity) == HV_STATS_AREA_PARENT &&
> +                           hv_status == HV_STATUS_INVALID_PARAMETER) {
> +                               pr_debug_once("%s: PARENT area type is unsupported\n",
> +                                             __func__);
> +                               *addr = NULL;
> +                               return 0;
> +                       }
> +
> +                       hv_status_debug(status, "\n");
> +                       return hv_result_to_errno(status);
>                 }
>
>                 ret = hv_call_deposit_pages(NUMA_NO_NODE,
> diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
> index bbdefe8a2e9c..56ababab57ce 100644
> --- a/drivers/hv/mshv_root_main.c
> +++ b/drivers/hv/mshv_root_main.c
> @@ -929,6 +929,9 @@ static int mshv_vp_stats_map(u64 partition_id, u32 vp_index,
>         if (err)
>                 goto unmap_self;
>
> +       if (!stats_pages[HV_STATS_AREA_PARENT])
> +               stats_pages[HV_STATS_AREA_PARENT] = stats_pages[HV_STATS_AREA_SELF];
> +
>         return 0;
>
>  unmap_self:
> --
> 2.34.1
>
>


-- 
Thanks
Tianyu Lan