drm/i915: Implement vm_ops->access for gdb access into mmaps
gdb uses ptrace() to peek and poke bytes of the target's address space. The driver must implement an vm_ops->access() handler or else gdb will be unable to inspect the pointer and report it as out-of-bounds. Worse than useless as it causes immediate suspicion of the valid GTT pointer, distracting the poor programmer trying to find his bug. v2: Write-protect readonly objects (Matthew). Testcase: igt/gem_mmap_gtt/ptrace Testcase: igt/gem_mmap_offset/ptrace Suggested-by: Kristian H. Kristensen <hoegsberg@google.com> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Matthew Auld <matthew.auld@intel.com> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Maciej Patelczyk <maciej.patelczyk@intel.com> Cc: Kristian H. Kristensen <hoegsberg@google.com> Reviewed-by: Matthew Auld <matthew.auld@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20200501145120.18830-1-chris@chris-wilson.co.uk
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