Re: [PATCH 1/2] drm/i915: Prevent a race during I915_GEM_MMAP ioctl with WC set

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 07/01/2019 08:56, Joonas Lahtinen wrote:
> Make sure the underlying VMA in the process address space is the
> same as it was during vm_mmap to avoid applying WC to wrong VMA.
> 
> A more long-term solution would be to have vm_mmap_locked variant
> in linux/mmap.h for when caller wants to hold mmap_sem for an
> extended duration.
> 
> Fixes: 1816f9236303 ("drm/i915: Support creation of unbound wc user mappings for objects")
> Reported-by: Adam Zabrocki <adamza@microsoft.com>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: <stable@vger.kernel.org> # v4.0+
> Cc: Akash Goel <akash.goel@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Cc: Adam Zabrocki <adamza@microsoft.com>
> ---
>   drivers/gpu/drm/i915/i915_gem.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 062c8395557c..f1d594a53978 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1680,6 +1680,15 @@ i915_gem_sw_finish_ioctl(struct drm_device *dev, void *data,
>   	return 0;
>   }
>   
> +static inline bool
> +match_gem_vma(struct vm_area_struct *vma, struct file *filp,
> +	      unsigned long addr, unsigned long size)
> +{
> +	return vma && vma->vm_file == filp &&
> +	       vma->vm_start == addr &&
> +	       (vma->vm_end - vma->vm_start) == size;
> +}
> +
>   /**
>    * i915_gem_mmap_ioctl - Maps the contents of an object, returning the address
>    *			 it is mapped to.
> @@ -1738,7 +1747,7 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
>   			return -EINTR;
>   		}
>   		vma = find_vma(mm, addr);
> -		if (vma)
> +		if (match_gem_vma(vma, obj->base.filp, addr, args->size))
>   			vma->vm_page_prot =
>   				pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
>   		else
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko