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The UEFI stub executes in the context of the firmware, which identity maps the available system RAM, which implies that only memory below 4 GB can be used for allocations on 32-bit architectures, even on [L]PAE capable hardware. So ignore any reported memory above 4 GB in efi_random_alloc(). This also fixes a reported build problem on ARM under -Os, where the 64-bit logical shift relies on a software routine that the ARM decompressor does not provide. A second [minor] issue is also fixed, where the '+ 1' is moved out of the shift, where it belongs: the reason for its presence is that a memory region where start == end should count as a single slot, given that 'end' takes the desired size and alignment of the allocation into account. To clarify the code in this regard, rename start/end to 'first_slot' and 'last_slot', respectively, and introduce 'region_end' to describe the last usable address of the current region. Reported-by: Arnd Bergmann <[email protected]> Signed-off-by: Ard Biesheuvel <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Matt Fleming <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: [email protected] Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]>