linux-kernel - Re: [PATCH v7 5/7] Drivers: hv: Improve region overlap detection in partition create

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Message-ID: <2c853152-c2f8-49c6-a16c-be8aa1b59234@linux.microsoft.com>
Date: Wed, 3 Dec 2025 10:58:12 -0800
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>,
 kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
 decui@...rosoft.com
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 5/7] Drivers: hv: Improve region overlap detection in
 partition create

On 11/25/2025 6:09 PM, Stanislav Kinsburskii wrote:
> Refactor region overlap check in mshv_partition_create_region to use
> mshv_partition_region_by_gfn for both start and end guest PFNs, replacing
> manual iteration.
> 
> This is a cleaner approach that leverages existing functionality to
> accurately detect overlapping memory regions.
> 
> Signed-off-by: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
> ---
>  drivers/hv/mshv_root_main.c |    8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
> index 5dfb933da981..ae600b927f49 100644
> --- a/drivers/hv/mshv_root_main.c
> +++ b/drivers/hv/mshv_root_main.c
> @@ -1086,13 +1086,9 @@ static int mshv_partition_create_region(struct mshv_partition *partition,
>  	u64 nr_pages = HVPFN_DOWN(mem->size);
>  
>  	/* Reject overlapping regions */
> -	hlist_for_each_entry(rg, &partition->pt_mem_regions, hnode) {
> -		if (mem->guest_pfn + nr_pages <= rg->start_gfn ||
> -		    rg->start_gfn + rg->nr_pages <= mem->guest_pfn)
> -			continue;
> -
> +	if (mshv_partition_region_by_gfn(partition, mem->guest_pfn) ||
> +	    mshv_partition_region_by_gfn(partition, mem->guest_pfn + nr_pages - 1))
>  		return -EEXIST;

This logic does not work. I fixed this check in
ba9eb9b86d23 mshv: Fix create memory region overlap check

This change would just be reverting that fix.

Consider an existing region at 0x2000 of size 0x1000. The user
tries to map a new region at 0x1000 of size 0x3000. Since the new region
starts before and ends after the existing region, the overlap would not
be detected by this logic. It just checks if an existing region contains
0x1000 or 0x4000 - 1 which it does not. This is why a manual iteration
here is needed.

> -	}
>  
>  	rg = mshv_region_create(mem->guest_pfn, nr_pages,
>  				mem->userspace_addr, mem->flags,
> 
>