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x86/cpu_entry_area: Prevent wraparound in setup_cpu_entry_area_ptes() on 32bit 

The loop which populates the CPU entry area PMDs can wrap around on 32bit
machines when the number of CPUs is small.

It worked wonderful for NR_CPUS=64 for whatever reason and the moron who
wrote that code did not bother to test it with !SMP.

Check for the wraparound to fix it.

Fixes: 92a0f81d89 ("x86/cpu_entry_area: Move it out of the fixmap")
Reported-by: kernel test robot <fengguang.wu@intel.com>
Signed-off-by: Thomas "Feels stupid" Gleixner <tglx@linutronix.de>
Tested-by: Borislav Petkov <bp@alien8.de>
This commit is contained in:
Thomas Gleixner 2017-12-23 19:45:11 +01:00
parent 613e396bc0
commit f6c4fd506c
1 changed files with 2 additions and 1 deletions
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3
arch/x86/mm/cpu_entry_area.c
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@ -122,7 +122,8 @@ static __init void setup_cpu_entry_area_ptes(void)
start = CPU_ENTRY_AREA_BASE;
end = start + CPU_ENTRY_AREA_MAP_SIZE;
for (; start < end; start += PMD_SIZE)
/* Careful here: start + PMD_SIZE might wrap around */
for (; start < end && start >= CPU_ENTRY_AREA_BASE; start += PMD_SIZE)
populate_extra_pte(start);
#endif
}