Messages in this thread | | | Date | Fri, 4 Jan 2013 13:59:33 -0800 | Subject | Re: [PATCH v7u1 31/31] x86, 64bit, mm: hibernate use generic mapping_init | From | Yinghai Lu <> |
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On Fri, Jan 4, 2013 at 3:43 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote: > On Thursday, January 03, 2013 04:48:51 PM Yinghai Lu wrote: >> Make it only map range in pfn_mapped array. > > Can you please explain why that should be sufficient?
It is needed.
http://git.kernel.org/?p=linux/kernel/git/tip/tip.git;a=commitdiff;h=66520ebc2df3fe52eb4792f8101fac573b766baf
Subject: [PATCH] x86, mm: Only direct map addresses that are marked as E820_RAM
Currently direct mappings are created for [ 0 to max_low_pfn<<PAGE_SHIFT ) and [ 4GB to max_pfn<<PAGE_SHIFT ), which may include regions that are not backed by actual DRAM. This is fine for holes under 4GB which are covered by fixed and variable range MTRRs to be UC. However, we run into trouble on higher memory addresses which cannot be covered by MTRRs.
Our system with 1TB of RAM has an e820 that looks like this:
BIOS-e820: [mem 0x0000000000000000-0x00000000000983ff] usable BIOS-e820: [mem 0x0000000000098400-0x000000000009ffff] reserved BIOS-e820: [mem 0x00000000000d0000-0x00000000000fffff] reserved BIOS-e820: [mem 0x0000000000100000-0x00000000c7ebffff] usable BIOS-e820: [mem 0x00000000c7ec0000-0x00000000c7ed7fff] ACPI data BIOS-e820: [mem 0x00000000c7ed8000-0x00000000c7ed9fff] ACPI NVS BIOS-e820: [mem 0x00000000c7eda000-0x00000000c7ffffff] reserved BIOS-e820: [mem 0x00000000fec00000-0x00000000fec0ffff] reserved BIOS-e820: [mem 0x00000000fee00000-0x00000000fee00fff] reserved BIOS-e820: [mem 0x00000000fff00000-0x00000000ffffffff] reserved BIOS-e820: [mem 0x0000000100000000-0x000000e037ffffff] usable BIOS-e820: [mem 0x000000e038000000-0x000000fcffffffff] reserved BIOS-e820: [mem 0x0000010000000000-0x0000011ffeffffff] usable
and so direct mappings are created for huge memory hole between 0x000000e038000000 to 0x0000010000000000. Even though the kernel never generates memory accesses in that region, since the page tables mark them incorrectly as being WB, our (AMD) processor ends up causing a MCE while doing some memory bookkeeping/optimizations around that area.
This patch iterates through e820 and only direct maps ranges that are marked as E820_RAM, and keeps track of those pfn ranges. 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.
> > Have you tested it? >
No
will update to
Subject: [PATCH] x86, 64bit, mm: hibernate use generic mapping_init
We should not set mapping for all under max_pfn. That causes same problem that is fixed by x86, mm: Only direct map addresses that are marked as E820_RAM
Make it only map range in pfn_mapped array.
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