Messages in this thread | | | Date | Wed, 14 Feb 2024 11:57:32 -0800 | From | Nicolin Chen <> | Subject | Re: [PATCH v1 0/2] nvme-pci: Fix dma-iommu mapping failures when PAGE_SIZE=64KB |
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Hi Will,
On Wed, Feb 14, 2024 at 04:41:38PM +0000, Will Deacon wrote: > Hi Nicolin, > > On Tue, Feb 13, 2024 at 01:53:55PM -0800, Nicolin Chen wrote: > > It's observed that an NVME device is causing timeouts when Ubuntu boots > > with a kernel configured with PAGE_SIZE=64KB due to failures in swiotlb: > > systemd[1]: Started Journal Service. > > => nvme 0000:00:01.0: swiotlb buffer is full (sz: 327680 bytes), total 32768 (slots), used 32 (slots) > > note: journal-offline[392] exited with irqs disabled > > note: journal-offline[392] exited with preempt_count 1 > > > > An NVME device under a PCIe bus can be behind an IOMMU, so dma mappings > > going through dma-iommu might be also redirected to swiotlb allocations. > > Similar to dma_direct_max_mapping_size(), dma-iommu should implement its > > dma_map_ops->max_mapping_size to return swiotlb_max_mapping_size() too. > > > > Though an iommu_dma_max_mapping_size() is a must, it alone can't fix the > > issue. The swiotlb_max_mapping_size() returns 252KB, calculated from the > > default pool 256KB subtracted by min_align_mask NVME_CTRL_PAGE_SIZE=4KB, > > while dma-iommu can roundup a 252KB mapping to 256KB at its "alloc_size" > > when PAGE_SIZE=64KB via iova->granule that is often set to PAGE_SIZE. So > > this mismatch between NVME_CTRL_PAGE_SIZE=4KB and PAGE_SIZE=64KB results > > in a similar failure, though its signature has a fixed size "256KB": > > systemd[1]: Started Journal Service. > > => nvme 0000:00:01.0: swiotlb buffer is full (sz: 262144 bytes), total 32768 (slots), used 128 (slots) > > note: journal-offline[392] exited with irqs disabled > > note: journal-offline[392] exited with preempt_count 1 > > > > Both failures above occur to NVME behind IOMMU when PAGE_SIZE=64KB. They > > were likely introduced for the security feature by: > > commit 82612d66d51d ("iommu: Allow the dma-iommu api to use bounce buffers"), > > > > So, this series bundles two fixes together against that. They should be > > taken at the same time to entirely fix the mapping failures. > > It's a bit of a shot in the dark, but I've got a pending fix to some of > the alignment handling in swiotlb. It would be interesting to know if > patch 1 has any impact at all on your NVME allocations: > > https://lore.kernel.org/r/20240205190127.20685-1-will@kernel.org
I applied these three patches locally for a test.
Though I am building with a v6.6 kernel, I see some warnings: from kernel/dma/swiotlb.c:26: kernel/dma/swiotlb.c: In function ‘swiotlb_area_find_slots’: /include/linux/minmax.h:21:35: warning: comparison of distinct pointer types lacks a cast 21 | (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1))) | ^~ /include/linux/minmax.h:27:18: note: in expansion of macro ‘__typecheck’ 27 | (__typecheck(x, y) && __no_side_effects(x, y)) | ^~~~~~~~~~~ /include/linux/minmax.h:37:31: note: in expansion of macro ‘__safe_cmp’ 37 | __builtin_choose_expr(__safe_cmp(x, y), \ | ^~~~~~~~~~ /include/linux/minmax.h:75:25: note: in expansion of macro ‘__careful_cmp’ 75 | #define max(x, y) __careful_cmp(x, y, >) | ^~~~~~~~~~~~~ kernel/dma/swiotlb.c:1007:26: note: in expansion of macro ‘max’ 1007 | stride = max(stride, PAGE_SHIFT - IO_TLB_SHIFT + 1); | ^~~
Replacing with a max_t() can fix these.
And it seems to get worse, as even a 64KB mapping is failing: [ 0.239821] nvme 0000:00:01.0: swiotlb buffer is full (sz: 65536 bytes), total 32768 (slots), used 0 (slots)
With a printk, I found the iotlb_align_mask isn't correct: swiotlb_area_find_slots:alloc_align_mask 0xffff, iotlb_align_mask 0x800
But fixing the iotlb_align_mask to 0x7ff still fails the 64KB mapping..
Thanks Nicolin
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