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    Subject[PATCH 5.4 126/138] io-mapping: indicate mapping failure
    Date
    From: Michael J. Ruhl <michael.j.ruhl@intel.com>

    commit e0b3e0b1a04367fc15c07f44e78361545b55357c upstream.

    The !ATOMIC_IOMAP version of io_maping_init_wc will always return
    success, even when the ioremap fails.

    Since the ATOMIC_IOMAP version returns NULL when the init fails, and
    callers check for a NULL return on error this is unexpected.

    During a device probe, where the ioremap failed, a crash can look like
    this:

    BUG: unable to handle page fault for address: 0000000000210000
    #PF: supervisor write access in kernel mode
    #PF: error_code(0x0002) - not-present page
    Oops: 0002 [#1] PREEMPT SMP
    CPU: 0 PID: 177 Comm:
    RIP: 0010:fill_page_dma [i915]
    gen8_ppgtt_create [i915]
    i915_ppgtt_create [i915]
    intel_gt_init [i915]
    i915_gem_init [i915]
    i915_driver_probe [i915]
    pci_device_probe
    really_probe
    driver_probe_device

    The remap failure occurred much earlier in the probe. If it had been
    propagated, the driver would have exited with an error.

    Return NULL on ioremap failure.

    [akpm@linux-foundation.org: detect ioremap_wc() errors earlier]

    Fixes: cafaf14a5d8f ("io-mapping: Always create a struct to hold metadata about the io-mapping")
    Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
    Cc: Mike Rapoport <rppt@linux.ibm.com>
    Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
    Cc: Chris Wilson <chris@chris-wilson.co.uk>
    Cc: Daniel Vetter <daniel@ffwll.ch>
    Cc: <stable@vger.kernel.org>
    Link: http://lkml.kernel.org/r/20200721171936.81563-1-michael.j.ruhl@intel.com
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    include/linux/io-mapping.h | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    --- a/include/linux/io-mapping.h
    +++ b/include/linux/io-mapping.h
    @@ -108,9 +108,12 @@ io_mapping_init_wc(struct io_mapping *io
    resource_size_t base,
    unsigned long size)
    {
    + iomap->iomem = ioremap_wc(base, size);
    + if (!iomap->iomem)
    + return NULL;
    +
    iomap->base = base;
    iomap->size = size;
    - iomap->iomem = ioremap_wc(base, size);
    #if defined(pgprot_noncached_wc) /* archs can't agree on a name ... */
    iomap->prot = pgprot_noncached_wc(PAGE_KERNEL);
    #elif defined(pgprot_writecombine)

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