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

[Boris Brezillon]

On Mon, 22 Jun 2026 23:57:17 +0200
"Christian A. Ehrhardt" <lk@xxxxxxx> wrote:

> In the ->huge_fault handler do not install a PMD huge page
> mapping if the huge page exceeds the boundaries of the VMA.
> 
> All other ->huge_fault handlers have similar checks and the
> resulting mapping will trigger a VM_BUG_ON_VMA() if it ever
> reaches copy_pmd_range().
> 
> Cc: Pedro Demarchi Gomes <pedrodemargomes@xxxxxxxxx>
> Cc: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: fc3bbf34e643 ("drm/shmem-helper: Fix huge page mapping in fault handler")
> Signed-off-by: Christian A. Ehrhardt <lk@xxxxxxx>

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

> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index c989459eb215..00807039f8d7 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -597,9 +597,13 @@ static vm_fault_t try_insert_pfn(struct vm_fault *vmf, unsigned int order,
>  #ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP
>  	} else if (order == PMD_ORDER) {
>  		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(pfn_to_page(pfn)))) {
>  			vm_fault_t ret;
>