Re: [PATCH] drm/xe: Unmap userptr in MMU invalidation notifier

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

On Fri, Apr 26, 2024 at 04:32:36PM -0700, Matthew Brost wrote:
> To be secure, when a userptr is invalidated the pages should be dma
> unmapped ensuring the device can no longer touch the invalidated pages.
> 
> Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
> Fixes: 12f4b58a37f4 ("drm/xe: Use hmm_range_fault to populate user pages")
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: stable@vger.kernel.org # 6.8
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_vm.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index dfd31b346021..964a5b4d47d8 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -637,6 +637,9 @@ static bool vma_userptr_invalidate(struct mmu_interval_notifier *mni,
>  		XE_WARN_ON(err);
>  	}
>  
> +	if (userptr->sg)
> +		xe_hmm_userptr_free_sg(uvma);
> +

I thought about this a bit, I think here we only dma unmap the SG, not
free it. Freeing it could cause a current bind walk to access corrupt
memory. Freeing can be deferred to the next attempt to bind the userptr
or userptr destroy.

Matt

>  	trace_xe_vma_userptr_invalidate_complete(vma);
>  
>  	return true;
> -- 
> 2.34.1
>