Re: [PATCH v2] drm/gpusvm: Zero HMM PFNs before scanning ranges

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Jul 21, 2026 at 09:29:56AM -0700, Stanislav Kinsburskii wrote:
> drm_gpusvm_check_pages() and drm_gpusvm_scan_mm() asks HMM to report the
> current CPU page-table state without faulting missing entries by leaving
> default_flags set to zero. The HMM PFN array is still caller-owned input/output
> state, and the framework may preserve input bits while filling entries. It is
> not safe for the caller to hand HMM an uninitialized array and then treat
> entries without HMM_PFN_VALID as an authoritative unpopulated result.
> 
> Use kvcalloc() for the temporary PFN array so entries that are not
> reported as valid start from the documented zero state. This prevents
> random stack or heap contents from being interpreted as HMM PFN flags or
> PFN values during the scan.
> 
> Fixes: f1d08a586482 ("drm/gpusvm: Introduce a function to scan the current migration state")
> Cc: stable@vger.kernel.org
> Signed-off-by: Stanislav Kinsburskii <skinsburskii@gmail.com>
> ---
>  drivers/gpu/drm/drm_gpusvm.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
> index ca234fd2c491..6ca6e68be5a6 100644
> --- a/drivers/gpu/drm/drm_gpusvm.c
> +++ b/drivers/gpu/drm/drm_gpusvm.c
> @@ -708,7 +708,7 @@ static bool drm_gpusvm_check_pages(struct drm_gpusvm *gpusvm,
>  
>  	mmap_assert_locked(gpusvm->mm);
>  
> -	pfns = kvmalloc_array(npages, sizeof(*pfns), GFP_KERNEL);
> +	pfns = kvcalloc(npages, sizeof(*pfns), GFP_KERNEL);

This is different offending original patch:

99624bdff867 drm/gpusvm: Add support for GPU Shared Virtual Memory

>  	if (!pfns)
>  		return false;
>  
> @@ -780,7 +780,7 @@ enum drm_gpusvm_scan_result drm_gpusvm_scan_mm(struct drm_gpusvm_range *range,
>  	const struct dev_pagemap *other = NULL;
>  	int err, i;
>  
> -	pfns = kvmalloc_array(npages, sizeof(*pfns), GFP_KERNEL);
> +	pfns = kvcalloc(npages, sizeof(*pfns), GFP_KERNEL);

Hence I merged your v1 to drm-misc-fixes last night.

Can you repost with just the drm_gpusvm_check_pages fix?

Matt

>  	if (!pfns)
>  		return DRM_GPUSVM_SCAN_UNPOPULATED;
>  
> 
>