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Message-ID: <AANLkTimcJx1XMW3XHJD44EJpOnmMzM6KdMDZAs0Adjgr@mail.gmail.com>
Date: Thu, 10 Jun 2010 13:14:57 -0600
From: Brian Gordon <legerde@...il.com>
To: Chris Friesen <cfriesen@...tel.com>
Cc: Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: Aerospace and linux
Thank you both. This has been very helpful for me.
I think I read two conclusions:
1) R/O is a small percentage of RAM
2) To cover this small precentage would be non-trivial
Thank you both very much for your time and knowledge, I'll move along now.
On Thu, Jun 10, 2010 at 12:46 PM, Chris Friesen <cfriesen@...tel.com> wrote:
> On 06/10/2010 12:38 PM, Brian Gordon wrote:
>
>> On the more exotic end, I have also seen systems that have dual
>> redundant processors / memories. Then they add compare logic between
>> the redundant processors that compare most pins each clock cycle. If
>> any pins are not identical at a clock cycle, then something has gone
>> wrong (SEU, hardware failure, etc..)
>
> Some phone switches do this. Some of them also have at least two copies
> of everything in memory and will do transactional operations that can be
> rolled back if there is a hardware glitch.
>
>> So, some pages of RAM are going to be read-only and the data in those
>> pages came from some source (file system?). Can anyone describe a
>> high level strategy to occasionaly provide some coverage of this data?
>
>> So far I have thought about page descriptors adding an MD5 hash
>> whenever they are read-only and first being "loaded/mapped?" and then
>> a background daemon could occasionaly verify.
>
> Makes sense to me. You might also pick an on-disk format with extra
> checksumming so you could compare the on-disk checksum with the
> in-memory checksum.
>
> Chris
>
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