6.6-stable review patch. If anyone has any objections, please let me know.
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From: Timur Tabi ttabi@nvidia.com
[ Upstream commit 04d98b3452331fa53ec3b698b66273af6ef73288 ]
The flush page DMA address is stored in a special register that is not associated with the GPU's standard DMA range. For example, on Turing, the GPU's MMU can handle 47-bit addresses, but the flush page address register is limited to 40 bits.
At the point during device initialization when the flush page is allocated, the DMA mask is still at its default of 32 bits. So even though it's unlikely that the flush page could exist above a 40-bit address, the dma_map_page() call could fail, e.g. if IOMMU is disabled and the address is above 32 bits. The simplest way to achieve all constraints is to allocate the page in the DMA32 zone. Since the flush page is literally just a page, this is an acceptable limitation. The alternative is to temporarily set the DMA mask to 40 (or 52 for Hopper and later) bits, but that could have unforseen side effects.
In situations where the flush page is allocated above 32 bits and IOMMU is disabled, you will get an error like this:
nouveau 0000:65:00.0: DMA addr 0x0000000107c56000+4096 overflow (mask ffffffff, bus limit 0).
Fixes: 5728d064190e ("drm/nouveau/fb: handle sysmem flush page from common code") Signed-off-by: Timur Tabi ttabi@nvidia.com Reviewed-by: Lyude Paul lyude@redhat.com Signed-off-by: Lyude Paul lyude@redhat.com Link: https://patch.msgid.link/20251113230323.1271726-1-ttabi@nvidia.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/nouveau/nvkm/subdev/fb/base.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/fb/base.c b/drivers/gpu/drm/nouveau/nvkm/subdev/fb/base.c index 8a286a9349ac6..7ce1b65e2c1c2 100644 --- a/drivers/gpu/drm/nouveau/nvkm/subdev/fb/base.c +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/fb/base.c @@ -279,7 +279,7 @@ nvkm_fb_ctor(const struct nvkm_fb_func *func, struct nvkm_device *device, mutex_init(&fb->tags.mutex);
if (func->sysmem.flush_page_init) { - fb->sysmem.flush_page = alloc_page(GFP_KERNEL | __GFP_ZERO); + fb->sysmem.flush_page = alloc_page(GFP_KERNEL | GFP_DMA32 | __GFP_ZERO); if (!fb->sysmem.flush_page) return -ENOMEM;