From: Tianyu Lan Tianyu.Lan@microsoft.com

commit 82806744fd7dde603b64c151eeddaa4ee62193fd upstream.

swiotlb_find_slots() skips slots according to io tlb aligned mask calculated from min aligned mask and original physical address offset. This affects max mapping size. The mapping size can't achieve the IO_TLB_SEGSIZE * IO_TLB_SIZE when original offset is non-zero. This will cause system boot up failure in Hyper-V Isolation VM where swiotlb force is enabled. Scsi layer use return value of dma_max_mapping_size() to set max segment size and it finally calls swiotlb_max_mapping_size(). Hyper-V storage driver sets min align mask to 4k - 1. Scsi layer may pass 256k length of request buffer with 0~4k offset and Hyper-V storage driver can't get swiotlb bounce buffer via DMA API. Swiotlb_find_slots() can't find 256k length bounce buffer with offset. Make swiotlb_max_mapping _size() take min align mask into account.

Signed-off-by: Tianyu Lan Tianyu.Lan@microsoft.com Signed-off-by: Christoph Hellwig hch@lst.de Signed-off-by: Rishabh Bhatnagar risbhat@amazon.com --- kernel/dma/swiotlb.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 018f140aaaf4..a9849670bdb5 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -709,7 +709,18 @@ dma_addr_t swiotlb_map(struct device *dev, phys_addr_t paddr, size_t size,

size_t swiotlb_max_mapping_size(struct device *dev) { - return ((size_t)IO_TLB_SIZE) * IO_TLB_SEGSIZE; + int min_align_mask = dma_get_min_align_mask(dev); + int min_align = 0; + + /* + * swiotlb_find_slots() skips slots according to + * min align mask. This affects max mapping size. + * Take it into acount here. + */ + if (min_align_mask) + min_align = roundup(min_align_mask, IO_TLB_SIZE); + + return ((size_t)IO_TLB_SIZE) * IO_TLB_SEGSIZE - min_align; }

bool is_swiotlb_active(struct device *dev)