Messages in this thread | | | Date | Thu, 17 Oct 2013 13:39:20 -0700 | Subject | Re: Corrupted low memory in v3.9+ | From | Olof Johansson <> |
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On Thu, Oct 17, 2013 at 12:39 PM, H. Peter Anvin <hpa@linux.intel.com> wrote: > On 10/17/2013 11:57 AM, Olof Johansson wrote: >> >> And the low memory checker never even ran before, since it had nothing >> to check. Earlier the lower reserved region would be included in the >> e820-reserved area if I read the code correctly, and now it's just >> marked reserved by the memblock code. >> >> I guess it could be argued either way whether this is a regression or >> not; but at the end of the day we now have systems where this warning >> pops when it didn't use to. :( >> > > I'm wondering if this is a problem with the low memory checker (the > residual value of which I have to admit to being skeptical of) or > something else.
There's a chance that it's a valid trip of the low-memory checker, i.e. that we do have a bios (or more likely smm), that stomps on that memory -- it was never checked for in the past and definitely not warned about. I'm not sure if that was intentional behavior or not (to not check this area), I lack history on the topic.
> Could you boot the box with "debug memblock=debug" and earlyprintk > turned on and send the boot output?
Ah, yes, I did verify that the first 64K were indeed set aside as reserved by doing just that:
[ 0.000000] MEMBLOCK configuration: [ 0.000000] memory size = 0x7c750000 reserved size = 0xb05000 [ 0.000000] memory.cnt = 0x6 [ 0.000000] memory[0x0] [0x00000000010000-0x0000000009ffff], 0x90000 bytes [ 0.000000] memory[0x1] [0x00000000100000-0x00000000efffff], 0xe00000 bytes [ 0.000000] memory[0x2] [0x00000001000000-0x0000001fffffff], 0x1f000000 bytes [ 0.000000] memory[0x3] [0x00000020200000-0x0000003fffffff], 0x1fe00000 bytes [ 0.000000] memory[0x4] [0x00000040200000-0x0000007c6bffff], 0x3c4c0000 bytes [ 0.000000] memory[0x5] [0x00000100000000-0x000001005fffff], 0x600000 bytes [ 0.000000] reserved.cnt = 0x2 [ 0.000000] reserved[0x0] [0x0000000009f000-0x000000000fffff], 0x61000 bytes [ 0.000000] reserved[0x1] [0x00000001000000-0x00000001aa3fff], 0xaa4000 bytes [ 0.000000] memblock_reserve: [0x00000000099000-0x0000000009f000] reserve_real_mode+0x61/0x87 [ 0.000000] Base memory trampoline at [ffff880000099000] 99000 size 24576 [ 0.000000] reserving inaccessible SNB gfx pages [ 0.000000] memblock_reserve: [0x00000000000000-0x00000000100000] setup_arch+0xa2d/0xa41 [...]
Unfortunately x86 doesn't keep the memblock structures around, so there's no way to verify after booting in debugfs, but based on the above it should have been reserved properly.
-Olof
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