linux-kernel - [PATCH] swiotlb: Max mapping size takes min align mask into account

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Date:   Tue, 10 May 2022 10:21:09 -0400
From:   Tianyu Lan <ltykernel@...il.com>
To:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, hch@...radead.org,
        m.szyprowski@...sung.com, robin.murphy@....com,
        michael.h.kelley@...rosoft.com
Cc:     Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        iommu@...ts.linux-foundation.org, linux-hyperv@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        vkuznets@...hat.com, konrad.wilk@...cle.com, hch@....de,
        parri.andrea@...il.com, thomas.lendacky@....com
Subject: [PATCH] swiotlb: Max mapping size takes min align mask into account

From: Tianyu Lan <Tianyu.Lan@...rosoft.com>

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@...rosoft.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 73a41cec9e38..0d6684ca7eab 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -743,7 +743,18 @@ 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)
-- 
2.25.1