linux-kernel - Re: [PATCH] drm/amdgpu: Pin buffer while vmap'ing exported dma-buf objects

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Message-ID: <7c2d8894-7eb5-4c86-a80a-935fcf24ef83@suse.de>
Date: Mon, 18 Aug 2025 14:46:03 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Christian König <christian.koenig@....com>,
 sumit.semwal@...aro.org, oushixiong@...inos.cn, alexander.deucher@....com,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, airlied@...il.com,
 simona@...ll.ch
Cc: dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
 linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
 amd-gfx@...ts.freedesktop.org
Subject: Re: [PATCH] drm/amdgpu: Pin buffer while vmap'ing exported dma-buf
 objects

Hi

Am 18.08.25 um 14:40 schrieb Christian König:
[...]
>> +static int amdgpu_dma_buf_vmap(struct dma_buf *dma_buf, struct iosys_map *map)
>> +{
>> +	struct drm_gem_object *obj = dma_buf->priv;
>> +	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
>> +	int ret;
>> +
>> +	/*
>> +	 * Pin to keep buffer in place while it's vmap'ed. The actual
>> +	 * location is not important as long as it's mapable.
> Yeah, exactly that won't work here. Most of the locations are not CPU accessible.
>
> You could use AMDGPU_GEM_DOMAIN_GTT, that should most likely work in all cases but isn't necessarily the most optimal solution.

No problem about that, but why not a bit more flexibility? When udl 
copies from the buffer, it is likely pinned to VRAM.

A bit mask of _CPU, _GTT, and _VRAM should work fine. The other domains 
are probably irrelevant for our use case.

Best regards
Thomas

>
> Regards,
> Christian.
>
>> +	 *
>> +	 * This code is required for exporting to GEM-SHMEM without S/G table.
>> +	 * Once GEM-SHMEM supports dynamic imports, it should be dropped.
>> +	 */
>> +	ret = amdgpu_bo_pin(bo, AMDGPU_GEM_DOMAIN_MASK);
>> +	if (ret)
>> +		return ret;
>> +	ret = drm_gem_dmabuf_vmap(dma_buf, map);
>> +	if (ret)
>> +		amdgpu_bo_unpin(bo);
>> +
>> +	return ret;
>> +}
>> +
>> +static void amdgpu_dma_buf_vunmap(struct dma_buf *dma_buf, struct iosys_map *map)
>> +{
>> +	struct drm_gem_object *obj = dma_buf->priv;
>> +	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
>> +
>> +	drm_gem_dmabuf_vunmap(dma_buf, map);
>> +	amdgpu_bo_unpin(bo);
>> +}
>> +
>>   const struct dma_buf_ops amdgpu_dmabuf_ops = {
>>   	.attach = amdgpu_dma_buf_attach,
>>   	.pin = amdgpu_dma_buf_pin,
>> @@ -294,8 +326,8 @@ const struct dma_buf_ops amdgpu_dmabuf_ops = {
>>   	.release = drm_gem_dmabuf_release,
>>   	.begin_cpu_access = amdgpu_dma_buf_begin_cpu_access,
>>   	.mmap = drm_gem_dmabuf_mmap,
>> -	.vmap = drm_gem_dmabuf_vmap,
>> -	.vunmap = drm_gem_dmabuf_vunmap,
>> +	.vmap = amdgpu_dma_buf_vmap,
>> +	.vunmap = amdgpu_dma_buf_vunmap,
>>   };
>>   
>>   /**

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)