Message-ID: <4DAF0DAA.5080608@redhat.com>
Date: Wed, 20 Apr 2011 12:45:30 -0400
From: Rik van Riel <riel@redhat.com>
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To: rwhitton@iee.org
CC: linux-kernel@vger.kernel.org
Subject: Re: Background memory scrubbing
References: <42558.1303286300@jupiter.eclipse.co.uk>
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On 04/20/2011 03:58 AM, Robert Whitton wrote:

> 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?

> This code works absolutely fine up to a short distance beyond the 16MB boundary (specifically it seems to always fail on my hardware at PFN 4105). At this point despite the fact that kmap returns a valid virtual address (and it is the virtual address that I expect - 0xffff880001009000) I get the kernel oops - "unable to handle kernel paging request".

Looks like you might be making some of the kernel code that
is running at that moment unreachable, leading to a kernel
page fault.
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