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

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Message-ID:
 <SN6PR02MB41573FF177210DBC95509B09D4D8A@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Tue, 2 Dec 2025 18:39:51 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>,
	"kys@...rosoft.com" <kys@...rosoft.com>, "haiyangz@...rosoft.com"
	<haiyangz@...rosoft.com>, "wei.liu@...nel.org" <wei.liu@...nel.org>,
	"decui@...rosoft.com" <decui@...rosoft.com>, Nuno Das Neves
	<nunodasneves@...ux.microsoft.com>
CC: "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v7 5/7] Drivers: hv: Improve region overlap detection in
 partition create

From: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com> Sent: Tuesday, November 25, 2025 6:09 PM
> 
> 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.

Unfortunately, the cleaner approach doesn't work. :-( It doesn't detect a
new region request that completely overlaps an existing region.

See https://lore.kernel.org/linux-hyperv/6a5f4ed5-63ae-4760-84c9-7290aaff8bd1@linux.microsoft.com/T/#ma91254da1900de61da520acb96c0de38c43562f6.
I couldn't see anything that prevents the scenario. Nuno created this 
patch less than a month ago: https://lore.kernel.org/linux-hyperv/1762467211-8213-2-git-send-email-nunodasneves@linux.microsoft.com/.

Michael

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