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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>