Re: [PATCH 5/5] drm/xe/query: use PAGE_SIZE as the minimum page alignment

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

On Wed, Feb 26, 2025 at 10:00:22AM +0800, Mingcong Bai via B4 Relay wrote:
> From: Mingcong Bai <jeffbai@aosc.io>
> 
> As this component hooks into userspace API, it should be assumed that it
> will play well with non-4K/64K pages.
> 
> Use `PAGE_SIZE' as the final reference for page alignment instead.
> 
> Cc: stable@vger.kernel.org
> Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
> Fixes: 801989b08aff ("drm/xe/uapi: Make constant comments visible in kernel doc")
> Tested-by: Mingcong Bai <jeffbai@aosc.io>
> Tested-by: Haien Liang <27873200@qq.com>
> Tested-by: Shirong Liu <lsr1024@qq.com>
> Tested-by: Haofeng Wu <s2600cw2@126.com>
> Link: https://github.com/FanFansfan/loongson-linux/commit/22c55ab3931c32410a077b3ddb6dca3f28223360
> Co-developed-by: Shang Yatsen <429839446@qq.com>
> Signed-off-by: Shang Yatsen <429839446@qq.com>
> Signed-off-by: Mingcong Bai <jeffbai@aosc.io>
> ---
>  drivers/gpu/drm/xe/xe_query.c | 2 +-
>  include/uapi/drm/xe_drm.h     | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_query.c b/drivers/gpu/drm/xe/xe_query.c
> index c059639613f7b548c168f808b7b7b354f1cf3c94..8a017c526942d1f2b401e8b9a4244e6083d7b1e5 100644
> --- a/drivers/gpu/drm/xe/xe_query.c
> +++ b/drivers/gpu/drm/xe/xe_query.c
> @@ -336,7 +336,7 @@ static int query_config(struct xe_device *xe, struct drm_xe_device_query *query)
>  		config->info[DRM_XE_QUERY_CONFIG_FLAGS] =
>  			DRM_XE_QUERY_CONFIG_FLAG_HAS_VRAM;
>  	config->info[DRM_XE_QUERY_CONFIG_MIN_ALIGNMENT] =
> -		xe->info.vram_flags & XE_VRAM_FLAGS_NEED64K ? SZ_64K : SZ_4K;
> +		xe->info.vram_flags & XE_VRAM_FLAGS_NEED64K ? SZ_64K : PAGE_SIZE;

We should probably assert or build a bug somewhere to ensure SZ_64K >=
PAGE_SIZE for future-proofing. Otherwise, I think the patch makes sense.
One more comment below.

>  	config->info[DRM_XE_QUERY_CONFIG_VA_BITS] = xe->info.va_bits;
>  	config->info[DRM_XE_QUERY_CONFIG_MAX_EXEC_QUEUE_PRIORITY] =
>  		xe_exec_queue_device_get_max_priority(xe);
> diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h
> index f62689ca861a4673b885629460c11d6f3bc6523d..db7cf904926ebd6789a29d620161ac051e59f13f 100644
> --- a/include/uapi/drm/xe_drm.h
> +++ b/include/uapi/drm/xe_drm.h
> @@ -394,7 +394,7 @@ struct drm_xe_query_mem_regions {
>   *    - %DRM_XE_QUERY_CONFIG_FLAG_HAS_VRAM - Flag is set if the device
>   *      has usable VRAM
>   *  - %DRM_XE_QUERY_CONFIG_MIN_ALIGNMENT - Minimal memory alignment
> - *    required by this device, typically SZ_4K or SZ_64K
> + *    required by this device, typically PAGE_SIZE.

So I think the kernel doc needs bit more updating here, how about:

Minimal memory alignment required by this device and the CPU. The
minimum page size for the device is usually SZ_4K or SZ_64K, while for
the CPU, it is PAGE_SIZE. This value is calculated by
max(min_gpu_page_size, PAGE_SIZE). This alignment is enforced on
buffer object allocations and VM binds.

Again welcome others CC'd suggestion on this updated kernel doc. 

Matt

>   *  - %DRM_XE_QUERY_CONFIG_VA_BITS - Maximum bits of a virtual address
>   *  - %DRM_XE_QUERY_CONFIG_MAX_EXEC_QUEUE_PRIORITY - Value of the highest
>   *    available exec queue priority
> 
> -- 
> 2.48.1
> 
>