Re: [PATCH] drm/panthor: Check VMA boundaries for PMD mappings

[Boris Brezillon <boris.brezillon@collabora.com>]

On Tue, 23 Jun 2026 20:19:42 +0200
"Christian A. Ehrhardt" <lk@c--e.de> wrote:

> When checking a different patch[1] sashiko AI pointed out that
> panthor needs the same fix[2]:
> 
> In the ->huge_fault handler do not install a PMD huge page
> mapping if the huge page exceeds the boundaries of the VMA.
> 
> [1] https://lore.kernel.org/lkml/20260622215718.1532689-1-lk@c--e.de/
> [2] https://sashiko.dev/#/patchset/20260622215718.1532689-1-lk%40c--e.de
> 
> Cc: Boris Brezillon <boris.brezillon@collabora.com>
> Cc: Steven Price <steven.price@arm.com>
> Cc: Liviu Dudau <liviu.dudau@arm.com>
> Fixes: 68cbf96b1e9b ("drm/panthor: Part ways with drm_gem_shmem_object")
> Signed-off-by: Christian A. Ehrhardt <lk@c--e.de>

I know the discussion is ongoing to decide what we should do about
these huge_fault() handlers, but I think it's worth getting this fix in
in the meantime.

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> ---
>  drivers/gpu/drm/panthor/panthor_gem.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> NOTE:
> The panthor version is only compile tested because I don't
> have the hardware. However, the code is identical to that
> fixed in [1] and I have a reproducer for that.
> 
> No need for for stable backports. The code is new in 7.1.
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index a1e2eb1ca7bb..54535bae2b0c 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -802,9 +802,13 @@ static vm_fault_t insert_page(struct vm_fault *vmf, unsigned int order, struct p
>  	} else if (order == PMD_ORDER) {
>  		unsigned long pfn = page_to_pfn(page);
>  		unsigned long paddr = pfn << PAGE_SHIFT;
> +		struct vm_area_struct *vma = vmf->vma;
> +		unsigned long start = ALIGN_DOWN(vmf->address, PMD_SIZE);
> +		unsigned long end = start + PMD_SIZE;
> +		bool in_range = vma->vm_start <= start && end <= vma->vm_end;
>  		bool aligned = (vmf->address & ~PMD_MASK) == (paddr & ~PMD_MASK);
>  
> -		if (aligned &&
> +		if (aligned && in_range &&
>  		    folio_test_pmd_mappable(page_folio(page))) {
>  			pfn &= PMD_MASK >> PAGE_SHIFT;
>  			return vmf_insert_pfn_pmd(vmf, pfn, vmf->flags & FAULT_FLAG_WRITE);