diff options
| author | Zhang Yanfei <zhangyanfei@cn.fujitsu.com> | 2013-05-10 09:57:07 +1000 |
|---|---|---|
| committer | Stephen Rothwell <sfr@canb.auug.org.au> | 2013-05-10 12:58:31 +1000 |
| commit | 3a539e09a723052219a53936c5efce63b9e593ef (patch) | |
| tree | f7eb85f94d097dbc88b8e8b3b11ae144a43b6636 /arch/x86/mm | |
| parent | d01afb88de926bb8d7ede57376f0add0ad22bc5c (diff) | |
x86: mm: add missing comments for initial kernel direct mapping
For some reason, comments below are lost:
- comments for init_range_memory_mapping()
- comments in init_mem_mapping that is helpful for reminding people
that the pagetable is setup top-down
The comments were written by Yinghai in his patch in
https://lkml.org/lkml/2012/11/28/620
Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'arch/x86/mm')
| -rw-r--r-- | arch/x86/mm/init.c | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c index fdc5dca14fb3..fed9993d0c5b 100644 --- a/arch/x86/mm/init.c +++ b/arch/x86/mm/init.c @@ -359,7 +359,17 @@ unsigned long __init_refok init_memory_mapping(unsigned long start, } /* - * would have hole in the middle or ends, and only ram parts will be mapped. + * We need to iterate through E820 memory map and create direct mappings + * for only E820_RAM and E820_KERN_RESERVED regions. We cannot simply + * create direct mappings for all pfns from [0 to max_low_pfn) and + * [4GB to max_pfn) because of possible memory holes in high addresses + * that cannot be marked as UC by fixed/variable range MTRRs. + * Depending on the alignment of E820 ranges, this may possibly result + * in using smaller size (i.e. 4K instead of 2M or 1G) page tables. + * + * init_mem_mapping call init_range_memory_mapping with big range. + * That range would have hole in the middle or ends, and only ram parts + * will be mapped in init_range_memory_mapping. */ static unsigned long __init init_range_memory_mapping( unsigned long r_start, @@ -419,6 +429,13 @@ void __init init_mem_mapping(void) max_pfn_mapped = 0; /* will get exact value next */ min_pfn_mapped = real_end >> PAGE_SHIFT; last_start = start = real_end; + + /* + * We start from the top (end of memory) and go to the bottom. + * The memblock_find_in_range gets us a block of RAM from the + * end of RAM in [min_pfn_mapped, max_pfn_mapped) as new pages + * for page table. + */ while (last_start > ISA_END_ADDRESS) { if (last_start > step_size) { start = round_down(last_start - 1, step_size); |