Re: Background memory scrubbing

[Pavel Machek <pavel@ucw.cz>]

Hi!

> >>>for each PFN from 256 to the highest valid PFN
> >>>{
> >>>if (pfn_valid(PFN))
> >>>{
> >>>page = pfn_to_page(PFN)
> >>>va = kmap(page)
> >>>atomic_scrub(va, PAGE_SIZE)
> >>>kunmap(page)
> >>>}
> >>>
> >>>sleep(for_a_while)
> >>>}
> >>
> >>What exactly does atomic_scrub do?
> >
> >atomic_scrub is part of the edac subsystem see arch/x86/include/asm/edac.h. It simply does a locked add of zero to each DWORD in the specified range.
> 
> I can think of only a few ways in which that could cause a
> kernel page fault.
> 
> One of the more obvious causes would be running into an
> area of kernel memory that is mapped read-only.  Writing
> to a page that is mapped read-only would cause a page
> fault :)

...also... you are actually making kernel use "self modifying code"
here. There  are CPU bugs in that area...  for example on K6.
								Pavel
-- 
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