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SubjectRe: broken memory chip -> software fix?
On Fri, 17 Aug 2001, David Madore wrote:

> Hi all.
>
> I have a broken bit in my memory - at address 0x04d5ae38 if you want
> to know the details (bit 29 of the double word there sometimes reads
> as 1 when it was written as 0, in particular if bit 15 is at 1). I
> discovered this by observing a one-bit corruption of some files, and
> diagnosed it by running memtest86.
>
> Now that I know the address, is there a way I can prevent Linux from
> using that region of memory in any way? The simplest and cleanest
> way, would be, I guess, for a userland process I would write to ask of
> the kernel to map permanently and unswappably the page at physical
> location 0x04d5a000 to its virtual address space. (Besides, that
> would let me play with that broken bit.)
>
> So: is there a way for a userland process (running at euid 0) to
> request of the kernel an explicit physical address to virtual address
> translation? If so, how? I would prefer not to have to patch the
> kernel, if at all possible.
>
> Thanks,
>

mmap(0x04d5a000, PAGE_SIZE, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_FIXED, fd,
^^^^ page boundary
0);

'MAP_FIXED' is your friend. This will take the offending page size
(0x1000) on x86, out of use and give it to you. 'fd' is initialized
by opening /dev/mem.

Cheers,
Dick Johnson

Penguin : Linux version 2.4.1 on an i686 machine (799.53 BogoMips).

I was going to compile a list of innovations that could be
attributed to Microsoft. Once I realized that Ctrl-Alt-Del
was handled in the BIOS, I found that there aren't any.


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