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    Subject[PATCH 4.19 48/49] powerpc/dma: Fix dma_map_ops::get_required_mask
    Date
    From: Alexey Kardashevskiy <aik@ozlabs.ru>

    commit 437ef802e0adc9f162a95213a3488e8646e5fc03 upstream.

    There are 2 problems with it:
    1. "<" vs expected "<<"
    2. the shift number is an IOMMU page number mask, not an address
    mask as the IOMMU page shift is missing.

    This did not hit us before f1565c24b596 ("powerpc: use the generic
    dma_ops_bypass mode") because we had additional code to handle bypass
    mask so this chunk (almost?) never executed.However there were
    reports that aacraid does not work with "iommu=nobypass".

    After f1565c24b596, aacraid (and probably others which call
    dma_get_required_mask() before setting the mask) was unable to enable
    64bit DMA and fall back to using IOMMU which was known not to work,
    one of the problems is double free of an IOMMU page.

    This fixes DMA for aacraid, both with and without "iommu=nobypass" in
    the kernel command line. Verified with "stress-ng -d 4".

    Fixes: 6a5c7be5e484 ("powerpc: Override dma_get_required_mask by platform hook and ops")
    Cc: stable@vger.kernel.org # v3.2+
    Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/20200908015106.79661-1-aik@ozlabs.ru
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/powerpc/kernel/dma-iommu.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/arch/powerpc/kernel/dma-iommu.c
    +++ b/arch/powerpc/kernel/dma-iommu.c
    @@ -100,7 +100,8 @@ static u64 dma_iommu_get_required_mask(s
    if (!tbl)
    return 0;

    - mask = 1ULL < (fls_long(tbl->it_offset + tbl->it_size) - 1);
    + mask = 1ULL << (fls_long(tbl->it_offset + tbl->it_size) +
    + tbl->it_page_shift - 1);
    mask += mask - 1;

    return mask;

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