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Mon, 27 Apr 2026 08:39:44 +0000 Message-ID: <0d55bb5b-a860-48cf-b415-e7b5d001fb9c@amd.com> Date: Mon, 27 Apr 2026 10:39:40 +0200 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 03/11] drm/amdgpu/gem: only enforce amdgpu_bo access checks on amdgpu_bo objects To: Jesse Zhang , amd-gfx@lists.freedesktop.org Cc: Alexander.Deucher@amd.com References: <20260427083543.1328533-1-Jesse.Zhang@amd.com> <20260427083543.1328533-3-Jesse.Zhang@amd.com> Content-Language: en-US From: =?UTF-8?Q?Christian_K=C3=B6nig?= In-Reply-To: <20260427083543.1328533-3-Jesse.Zhang@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: IA4P220CA0003.NAMP220.PROD.OUTLOOK.COM (2603:10b6:208:558::12) To PH7PR12MB5685.namprd12.prod.outlook.com (2603:10b6:510:13c::22) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH7PR12MB5685:EE_|SJ2PR12MB8955:EE_ X-MS-Office365-Filtering-Correlation-Id: 4985b4b0-091b-4cb6-2e75-08dea438885a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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For a bare drm_gem_object created via > drm_gem_private_object_init() with its own drm_gem_object_funcs (e.g. > the SDMA UMQ doorbell pool BO), Well big NAK to that approach. Why in the world would we want to create a GEM object directly through drm_gem_private_object_init()? Regards, Christian. > the cast yields a pointer to unrelated > memory. Whether that memory happens to look like a usermm or carry > AMDGPU_GEM_CREATE_NO_CPU_ACCESS set is a function of allocator state, > producing intermittent -EPERM returns from DRM_IOCTL_AMDGPU_GEM_MMAP. > > Gate the amdgpu_bo-specific check on gobj->funcs matching > amdgpu_gem_object_funcs, and resolve the mmap offset via the GEM > vma_node directly so the path works for any drm_gem_object backed by > this ioctl. > --- > drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 21 +++++++++++++++------ > 1 file changed, 15 insertions(+), 6 deletions(-) > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c > index 0071d6957828..ccb92088172c 100644 > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c > @@ -587,13 +587,22 @@ int amdgpu_mode_dumb_mmap(struct drm_file *filp, > if (!gobj) > return -ENOENT; > > - robj = gem_to_amdgpu_bo(gobj); > - if (amdgpu_ttm_tt_get_usermm(robj->tbo.ttm) || > - (robj->flags & AMDGPU_GEM_CREATE_NO_CPU_ACCESS)) { > - drm_gem_object_put(gobj); > - return -EPERM; > + /* > + * The amdgpu_bo-specific access checks below assume gobj is wrapped > + * in an amdgpu_bo. Bare drm_gem_object instances (e.g., the SDMA UMQ > + * doorbell pool BO created via drm_gem_private_object_init with its > + * own funcs) are not amdgpu_bo, so gem_to_amdgpu_bo would dereference > + * unrelated memory and intermittently return -EPERM. > + */ > + if (gobj->funcs == &amdgpu_gem_object_funcs) { > + robj = gem_to_amdgpu_bo(gobj); > + if (amdgpu_ttm_tt_get_usermm(robj->tbo.ttm) || > + (robj->flags & AMDGPU_GEM_CREATE_NO_CPU_ACCESS)) { > + drm_gem_object_put(gobj); > + return -EPERM; > + } > } > - *offset_p = amdgpu_bo_mmap_offset(robj); > + *offset_p = drm_vma_node_offset_addr(&gobj->vma_node); > drm_gem_object_put(gobj); > return 0; > }