Re: [PATCH v7u1 31/31] x86, 64bit, mm: hibernate use generic mapping_init

From: Rafael J. Wysocki
Date: Fri Jan 04 2013 - 17:01:50 EST

On Friday, January 04, 2013 01:59:33 PM Yinghai Lu wrote:
> On Fri, Jan 4, 2013 at 3:43 AM, Rafael J. Wysocki <rjw@xxxxxxx> 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.
> 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.



I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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