linux-kernel - Re: [PATCH v3 1/5] mshv: Only map vp->vp_stats

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Message-ID: <aMxRme0kxXwE_jul@skinsburskii.localdomain>
Date: Thu, 18 Sep 2025 11:38:17 -0700
From: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
To: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
	prapal@...ux.microsoft.com, easwar.hariharan@...ux.microsoft.com,
	tiala@...rosoft.com, anirudh@...rudhrb.com,
	paekkaladevi@...ux.microsoft.com, kys@...rosoft.com,
	haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com
Subject: Re: [PATCH v3 1/5] mshv: Only map vp->vp_stats_pages if on root
 scheduler

On Tue, Sep 16, 2025 at 04:44:18PM -0700, Nuno Das Neves wrote:
> This mapping is only used for checking if the dispatch thread is
> blocked. This is only relevant for the root scheduler, so check the
> scheduler type to determine whether to map/unmap these pages, instead of
> the current check, which is incorrect.
> 
> Signed-off-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
> Reviewed-by: Anirudh Rayabharam <anirudh@...rudhrb.com>
> Reviewed-by: Praveen K Paladugu <prapal@...ux.microsoft.com>
> Reviewed-by: Easwar Hariharan <easwar.hariharan@...ux.microsoft.com>
> Reviewed-by: Tianyu Lan <tiala@...rosoft.com>
> ---
>  drivers/hv/mshv_root_main.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
> index e3b2bd417c46..24df47726363 100644
> --- a/drivers/hv/mshv_root_main.c
> +++ b/drivers/hv/mshv_root_main.c
> @@ -934,7 +934,11 @@ mshv_partition_ioctl_create_vp(struct mshv_partition *partition,
>  			goto unmap_register_page;
>  	}
>  
> -	if (hv_parent_partition()) {
> +	/*
> +	 * This mapping of the stats page is for detecting if dispatch thread
> +	 * is blocked - only relevant for root scheduler
> +	 */
> +	if (hv_scheduler_type == HV_SCHEDULER_TYPE_ROOT) {
>  		ret = mshv_vp_stats_map(partition->pt_id, args.vp_index,
>  					stats_pages);
>  		if (ret)
> @@ -963,7 +967,7 @@ mshv_partition_ioctl_create_vp(struct mshv_partition *partition,
>  	if (mshv_partition_encrypted(partition) && is_ghcb_mapping_available())
>  		vp->vp_ghcb_page = page_to_virt(ghcb_page);
>  
> -	if (hv_parent_partition())
> +	if (hv_scheduler_type == HV_SCHEDULER_TYPE_ROOT)
>  		memcpy(vp->vp_stats_pages, stats_pages, sizeof(stats_pages));
>  
>  	/*
> @@ -986,7 +990,7 @@ mshv_partition_ioctl_create_vp(struct mshv_partition *partition,
>  free_vp:
>  	kfree(vp);
>  unmap_stats_pages:
> -	if (hv_parent_partition())
> +	if (hv_scheduler_type == HV_SCHEDULER_TYPE_ROOT)
>  		mshv_vp_stats_unmap(partition->pt_id, args.vp_index);
>  unmap_ghcb_page:
>  	if (mshv_partition_encrypted(partition) && is_ghcb_mapping_available()) {
> @@ -1740,7 +1744,7 @@ static void destroy_partition(struct mshv_partition *partition)
>  			if (!vp)
>  				continue;
>  
> -			if (hv_parent_partition())
> +			if (hv_scheduler_type == HV_SCHEDULER_TYPE_ROOT)
>  				mshv_vp_stats_unmap(partition->pt_id, vp->vp_index);
>  
>  			if (vp->vp_register_page) {

Acked-by: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>

> -- 
> 2.34.1
>