When low memory doesn't reach HIGHMEM_START (e.g. up to 256MB at PA=0 is common) and highmem is present above HIGHMEM_START (e.g. on Malta the RAM overlayed by the IO region is aliased at PA=0x90000000), max_low_pfn will be initially calculated very large and then clipped down to HIGHMEM_START. This causes crashes when reading /sys/kernel/mm/page_idle/bitmap (i.e. CONFIG_IDLE_PAGE_TRACKING=y) when highmem is disabled. pfn_valid() will compare against max_mapnr which is derived from max_low_pfn when there is no highend_pfn set up, and will return true for PFNs right up to HIGHMEM_START, even though they are beyond the end of low memory and no page structs will actually exist for these PFNs. This is fixed by skipping high memory regions when initially calculating max_low_pfn if highmem is disabled, so it doesn't get clipped too high. We also clip regions which overlap the highmem boundary when highmem is disabled, so that max_pfn doesn't extend into highmem either. Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Cc: Paul Burton <paul.burton@xxxxxxxxxx> Cc: linux-mips@xxxxxxxxxxxxxx --- arch/mips/kernel/setup.c | 13 +++++++++++++ 1 file changed, 13 insertions(+), 0 deletions(-) diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c index 0d57909d9026..f66e5ce505b2 100644 --- a/arch/mips/kernel/setup.c +++ b/arch/mips/kernel/setup.c @@ -368,6 +368,19 @@ static void __init bootmem_init(void) end = PFN_DOWN(boot_mem_map.map[i].addr + boot_mem_map.map[i].size); +#ifndef CONFIG_HIGHMEM + /* + * Skip highmem here so we get an accurate max_low_pfn if low + * memory stops short of high memory. + * If the region overlaps HIGHMEM_START, end is clipped so + * max_pfn excludes the highmem portion. + */ + if (start >= PFN_DOWN(HIGHMEM_START)) + continue; + if (end > PFN_DOWN(HIGHMEM_START)) + end = PFN_DOWN(HIGHMEM_START); +#endif + if (end > max_low_pfn) max_low_pfn = end; if (start < min_low_pfn) -- git-series 0.8.10
