On Tue, 2022-09-27 at 11:39 +1000, Alistair Popple wrote: > 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. Mhm, TBH I feel like this was going to happen eventually anyway but there's another reason for nouveau to start using the managed versions of these functions at some point > > > 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, > -- Cheers, Lyude Paul (she/her) Software Engineer at Red Hat
