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    Subject[PATCH] swiotlb: fix phys_addr_t overflow warning
    Date
    On architectures that have a larger dma_addr_t than phys_addr_t,
    the swiotlb_tbl_map_single() function truncates its return code
    in the failure path, making it impossible to identify the error
    later, as we compare to the original value:

    kernel/dma/swiotlb.c:551:9: error: implicit conversion from 'dma_addr_t' (aka 'unsigned long long') to 'phys_addr_t' (aka 'unsigned int') changes value from 18446744073709551615 to 4294967295 [-Werror,-Wconstant-conversion]
    return DMA_MAPPING_ERROR;

    Use an explicit typecast here to convert it to the narrower type,
    and use the same expression in the error handling later.

    Fixes: b907e20508d0 ("swiotlb: remove SWIOTLB_MAP_ERROR")
    Signed-off-by: Arnd Bergmann <arnd@arndb.de>
    ---
    I still think that reverting the original commit would have
    provided clearer semantics for this corner case, but at least
    this patch restores the correct behavior.
    ---
    drivers/xen/swiotlb-xen.c | 2 +-
    kernel/dma/swiotlb.c | 4 ++--
    2 files changed, 3 insertions(+), 3 deletions(-)

    diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
    index d53f3493a6b9..cfbe46785a3b 100644
    --- a/drivers/xen/swiotlb-xen.c
    +++ b/drivers/xen/swiotlb-xen.c
    @@ -402,7 +402,7 @@ static dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,

    map = swiotlb_tbl_map_single(dev, start_dma_addr, phys, size, dir,
    attrs);
    - if (map == DMA_MAPPING_ERROR)
    + if (map == (phys_addr_t)DMA_MAPPING_ERROR)
    return DMA_MAPPING_ERROR;

    dev_addr = xen_phys_to_bus(map);
    diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
    index e906ef2e6315..a3be651973ad 100644
    --- a/kernel/dma/swiotlb.c
    +++ b/kernel/dma/swiotlb.c
    @@ -548,7 +548,7 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
    if (!(attrs & DMA_ATTR_NO_WARN) && printk_ratelimit())
    dev_warn(hwdev, "swiotlb buffer is full (sz: %zd bytes), total %lu (slots), used %lu (slots)\n",
    size, io_tlb_nslabs, tmp_io_tlb_used);
    - return DMA_MAPPING_ERROR;
    + return (phys_addr_t)DMA_MAPPING_ERROR;
    found:
    io_tlb_used += nslots;
    spin_unlock_irqrestore(&io_tlb_lock, flags);
    @@ -666,7 +666,7 @@ bool swiotlb_map(struct device *dev, phys_addr_t *phys, dma_addr_t *dma_addr,
    /* Oh well, have to allocate and map a bounce buffer. */
    *phys = swiotlb_tbl_map_single(dev, __phys_to_dma(dev, io_tlb_start),
    *phys, size, dir, attrs);
    - if (*phys == DMA_MAPPING_ERROR)
    + if (*phys == (phys_addr_t)DMA_MAPPING_ERROR)
    return false;

    /* Ensure that the address returned is DMA'ble */
    --
    2.20.0
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