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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Tianyu Lan <Tianyu.Lan@microsoft.com>,
        Christoph Hellwig <hch@lst.de>,
        Rishabh Bhatnagar <risbhat@amazon.com>
Subject: [PATCH 5.15 38/83] swiotlb: max mapping size takes min align mask into account
Date:   Mon,  3 Oct 2022 09:11:03 +0200
Message-Id: <20221003070722.955669891@linuxfoundation.org>
In-Reply-To: <20221003070721.971297651@linuxfoundation.org>
References: <20221003070721.971297651@linuxfoundation.org>
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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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/dma/swiotlb.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -709,7 +709,18 @@ dma_addr_t swiotlb_map(struct device *de
 
 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)