Felix Kuehling <felix.kuehling@xxxxxxx> writes: > On 2022-09-26 17:35, Lyude Paul wrote: >> On Mon, 2022-09-26 at 16:03 +1000, Alistair Popple wrote: >>> When the module is unloaded or a GPU is unbound from the module it is >>> possible for device private pages to be left mapped in currently running >>> processes. This leads to a kernel crash when the pages are either freed >>> or accessed from the CPU because the GPU and associated data structures >>> and callbacks have all been freed. >>> >>> Fix this by migrating any mappings back to normal CPU memory prior to >>> freeing the GPU memory chunks and associated device private pages. >>> >>> Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx> >>> >>> --- >>> >>> I assume the AMD driver might have a similar issue. However I can't see >>> where device private (or coherent) pages actually get unmapped/freed >>> during teardown as I couldn't find any relevant calls to >>> devm_memunmap(), memunmap(), devm_release_mem_region() or >>> release_mem_region(). So it appears that ZONE_DEVICE pages are not being >>> properly freed during module unload, unless I'm missing something? >> I've got no idea, will poke Ben to see if they know the answer to this > > I guess we're relying on devm to release the region. Isn't the whole point of > using devm_request_free_mem_region that we don't have to remember to explicitly > release it when the device gets destroyed? I believe we had an explicit free > call at some point by mistake, and that caused a double-free during module > unload. See this commit for reference: Argh, thanks for that pointer. I was not so familiar with devm_request_free_mem_region()/devm_memremap_pages() as currently Nouveau explicitly manages that itself. > commit 22f4f4faf337d5fb2d2750aff13215726814273e > Author: Philip Yang <Philip.Yang@xxxxxxx> > Date: Mon Sep 20 17:25:52 2021 -0400 > > drm/amdkfd: fix svm_migrate_fini warning > Device manager releases device-specific resources when a driver > disconnects from a device, devm_memunmap_pages and > devm_release_mem_region calls in svm_migrate_fini are redundant. > It causes below warning trace after patch "drm/amdgpu: Split > amdgpu_device_fini into early and late", so remove function > svm_migrate_fini. > BUG: https://gitlab.freedesktop.org/drm/amd/-/issues/1718 > WARNING: CPU: 1 PID: 3646 at drivers/base/devres.c:795 > devm_release_action+0x51/0x60 > Call Trace: > ? memunmap_pages+0x360/0x360 > svm_migrate_fini+0x2d/0x60 [amdgpu] > kgd2kfd_device_exit+0x23/0xa0 [amdgpu] > amdgpu_amdkfd_device_fini_sw+0x1d/0x30 [amdgpu] > amdgpu_device_fini_sw+0x45/0x290 [amdgpu] > amdgpu_driver_release_kms+0x12/0x30 [amdgpu] > drm_dev_release+0x20/0x40 [drm] > release_nodes+0x196/0x1e0 > device_release_driver_internal+0x104/0x1d0 > driver_detach+0x47/0x90 > bus_remove_driver+0x7a/0xd0 > pci_unregister_driver+0x3d/0x90 > amdgpu_exit+0x11/0x20 [amdgpu] > Signed-off-by: Philip Yang <Philip.Yang@xxxxxxx> > Reviewed-by: Felix Kuehling <Felix.Kuehling@xxxxxxx> > Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx> > > Furthermore, I guess we are assuming that nobody is using the GPU when the > module is unloaded. As long as any processes have /dev/kfd open, you won't be > able to unload the module (except by force-unload). I suppose with ZONE_DEVICE > memory, we can have references to device memory pages even when user mode has > closed /dev/kfd. We do have a cleanup handler that runs in an MMU-free-notifier. > In theory that should run after all the pages in the mm_struct have been freed. > It releases all sorts of other device resources and needs the driver to still be > there. I'm not sure if there is anything preventing a module unload before the > free-notifier runs. I'll look into that. Right - module unload (or device unbind) is one of the other ways we can hit this issue in Nouveau at least. You can end up with ZONE_DEVICE pages mapped in a running process after the module has unloaded. Although now you mention it that seems a bit wrong - the pgmap refcount should provide some protection against that. Will have to look into that too. > Regards, > Felix > > >> >>> --- >>> drivers/gpu/drm/nouveau/nouveau_dmem.c | 48 +++++++++++++++++++++++++++- >>> 1 file changed, 48 insertions(+) >>> >>> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c >>> index 66ebbd4..3b247b8 100644 >>> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c >>> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c >>> @@ -369,6 +369,52 @@ nouveau_dmem_suspend(struct nouveau_drm *drm) >>> mutex_unlock(&drm->dmem->mutex); >>> } >>> +/* >>> + * Evict all pages mapping a chunk. >>> + */ >>> +void >>> +nouveau_dmem_evict_chunk(struct nouveau_dmem_chunk *chunk) >>> +{ >>> + unsigned long i, npages = range_len(&chunk->pagemap.range) >> PAGE_SHIFT; >>> + unsigned long *src_pfns, *dst_pfns; >>> + dma_addr_t *dma_addrs; >>> + struct nouveau_fence *fence; >>> + >>> + src_pfns = kcalloc(npages, sizeof(*src_pfns), GFP_KERNEL); >>> + dst_pfns = kcalloc(npages, sizeof(*dst_pfns), GFP_KERNEL); >>> + dma_addrs = kcalloc(npages, sizeof(*dma_addrs), GFP_KERNEL); >>> + >>> + migrate_device_range(src_pfns, chunk->pagemap.range.start >> PAGE_SHIFT, >>> + npages); >>> + >>> + for (i = 0; i < npages; i++) { >>> + if (src_pfns[i] & MIGRATE_PFN_MIGRATE) { >>> + struct page *dpage; >>> + >>> + /* >>> + * _GFP_NOFAIL because the GPU is going away and there >>> + * is nothing sensible we can do if we can't copy the >>> + * data back. >>> + */ >> You'll have to excuse me for a moment since this area of nouveau isn't one of >> my strongpoints, but are we sure about this? IIRC __GFP_NOFAIL means infinite >> retry, in the case of a GPU hotplug event I would assume we would rather just >> stop trying to migrate things to the GPU and just drop the data instead of >> hanging on infinite retries. >> >>> + dpage = alloc_page(GFP_HIGHUSER | __GFP_NOFAIL); >>> + dst_pfns[i] = migrate_pfn(page_to_pfn(dpage)); >>> + nouveau_dmem_copy_one(chunk->drm, >>> + migrate_pfn_to_page(src_pfns[i]), dpage, >>> + &dma_addrs[i]); >>> + } >>> + } >>> + >>> + nouveau_fence_new(chunk->drm->dmem->migrate.chan, false, &fence); >>> + migrate_device_pages(src_pfns, dst_pfns, npages); >>> + nouveau_dmem_fence_done(&fence); >>> + migrate_device_finalize(src_pfns, dst_pfns, npages); >>> + kfree(src_pfns); >>> + kfree(dst_pfns); >>> + for (i = 0; i < npages; i++) >>> + dma_unmap_page(chunk->drm->dev->dev, dma_addrs[i], PAGE_SIZE, DMA_BIDIRECTIONAL); >>> + kfree(dma_addrs); >>> +} >>> + >>> void >>> nouveau_dmem_fini(struct nouveau_drm *drm) >>> { >>> @@ -380,8 +426,10 @@ nouveau_dmem_fini(struct nouveau_drm *drm) >>> mutex_lock(&drm->dmem->mutex); >>> list_for_each_entry_safe(chunk, tmp, &drm->dmem->chunks, list) { >>> + nouveau_dmem_evict_chunk(chunk); >>> nouveau_bo_unpin(chunk->bo); >>> nouveau_bo_ref(NULL, &chunk->bo); >>> + WARN_ON(chunk->callocated); >>> list_del(&chunk->list); >>> memunmap_pages(&chunk->pagemap); >>> release_mem_region(chunk->pagemap.range.start,
