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

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Message-ID: <644647df-64d5-44eb-b7ac-13bd4b81d422@gmail.com>
Date: Fri, 5 Sep 2025 10:31:21 -0500
From: Praveen K Paladugu <praveenkpaladugu@...il.com>
To: Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
 linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: 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 7:43 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.
>
Is this behavior limited to VP stats? Or does it extend to other
stats (hypervisor, partition, etc) as well?

> This results a failure in module init. Instead of failing, gracefully
nit: s/This results in a failure during module init/> 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(-)
> 
> 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:

-- 
Regards,
Praveen K Paladugu