RE: [PATCH v4 5/5] iommu/dma: Force swiotlb_max_mapping_size on an untrusted device

[Michael Kelley <mhklinux@outlook.com>]

From: Will Deacon <will@kernel.org> Sent: Wednesday, February 21, 2024 3:35 AM
> 
> The swiotlb does not support a mapping size > swiotlb_max_mapping_size().
> On the other hand, with a 64KB PAGE_SIZE configuration, it's observed that
> an NVME device can map a size between 300KB~512KB, which certainly failed
> the swiotlb mappings, though the default pool of swiotlb has many slots:
>     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
> 
> Call trace:
> [    3.099918]  swiotlb_tbl_map_single+0x214/0x240
> [    3.099921]  iommu_dma_map_page+0x218/0x328
> [    3.099928]  dma_map_page_attrs+0x2e8/0x3a0
> [    3.101985]  nvme_prep_rq.part.0+0x408/0x878 [nvme]
> [    3.102308]  nvme_queue_rqs+0xc0/0x300 [nvme]
> [    3.102313]  blk_mq_flush_plug_list.part.0+0x57c/0x600
> [    3.102321]  blk_add_rq_to_plug+0x180/0x2a0
> [    3.102323]  blk_mq_submit_bio+0x4c8/0x6b8
> [    3.103463]  __submit_bio+0x44/0x220
> [    3.103468]  submit_bio_noacct_nocheck+0x2b8/0x360
> [    3.103470]  submit_bio_noacct+0x180/0x6c8
> [    3.103471]  submit_bio+0x34/0x130
> [    3.103473]  ext4_bio_write_folio+0x5a4/0x8c8
> [    3.104766]  mpage_submit_folio+0xa0/0x100
> [    3.104769]  mpage_map_and_submit_buffers+0x1a4/0x400
> [    3.104771]  ext4_do_writepages+0x6a0/0xd78
> [    3.105615]  ext4_writepages+0x80/0x118
> [    3.105616]  do_writepages+0x90/0x1e8
> [    3.105619]  filemap_fdatawrite_wbc+0x94/0xe0
> [    3.105622]  __filemap_fdatawrite_range+0x68/0xb8
> [    3.106656]  file_write_and_wait_range+0x84/0x120
> [    3.106658]  ext4_sync_file+0x7c/0x4c0
> [    3.106660]  vfs_fsync_range+0x3c/0xa8
> [    3.106663]  do_fsync+0x44/0xc0
> 
> Since untrusted devices might go down the swiotlb pathway with dma-iommu,
> these devices should not map a size larger than swiotlb_max_mapping_size.
> 
> To fix this bug, add iommu_dma_max_mapping_size() for untrusted devices to
> take into account swiotlb_max_mapping_size() v.s. iova_rcache_range() from
> the iommu_dma_opt_mapping_size().
> 
> Fixes: 82612d66d51d ("iommu: Allow the dma-iommu api to use bounce buffers")
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> Link: https://lore.kernel.org/all/ee51a3a5c32cf885b18f6416171802669f4a718a.1707851466.git.nicolinc@nvidia.com/
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  drivers/iommu/dma-iommu.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 50ccc4f1ef81..7d1a20da6d94 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1706,6 +1706,13 @@ static size_t
> iommu_dma_opt_mapping_size(void)
>  	return iova_rcache_range();
>  }
> 
> +static size_t iommu_dma_max_mapping_size(struct device *dev)
> +{
> +	if (is_swiotlb_active(dev) && dev_is_untrusted(dev))
> +		return swiotlb_max_mapping_size(dev);
> +	return SIZE_MAX;
> +}
> +

In this [1] email, Nicolin had a version of this function that incorporated
the IOMMU granule.  For granules bigger than 4K, I think that's needed
so that when IOMMU code sets the swiotlb alloc_align_mask to the
IOMMU granule - 1, the larger offset plus the size won't exceed the
max number of slots.  swiotlb_max_mapping_size() by itself may
return a value that's too big when alloc_align_mask is used.

Michael

[1] https://lore.kernel.org/linux-iommu/SN6PR02MB415727E61B5295C259CCB268D4512@SN6PR02MB4157.namprd02.prod.outlook.com/T/#m14dd359c5a4dd13e6cb0c35cf94f8d746257ae48


>  static const struct dma_map_ops iommu_dma_ops = {
>  	.flags			= DMA_F_PCI_P2PDMA_SUPPORTED,
>  	.alloc			= iommu_dma_alloc,
> @@ -1728,6 +1735,7 @@ static const struct dma_map_ops iommu_dma_ops = {
>  	.unmap_resource		= iommu_dma_unmap_resource,
>  	.get_merge_boundary	= iommu_dma_get_merge_boundary,
>  	.opt_mapping_size	= iommu_dma_opt_mapping_size,
> +	.max_mapping_size       = iommu_dma_max_mapping_size,
>  };
> 
>  /*
> --
> 2.44.0.rc0.258.g7320e95886-goog