В сообщении от Wednesday 26 December 2007 12:17:56 Arjan van de Ven написал(а):
> On Wed, 26 Dec 2007 00:09:57 +0100
> Pavel Machek <[email protected]> wrote:
>
> > On Sat 2007-12-22 12:09:59, Arjan van de Ven wrote:
> > > On Tue, 18 Dec 2007 17:06:24 +0000
>
> > > memtest86+ does various magic to basically bypass the caches (by
> > > disabling them ;-)... Doing that in a live kernel situation, and
> > > from userspace to boot...... that's... and issue.
> >
> > Are you sure? I always assumed that memtest just used patterns bigger
> > than L1/L2 caches...
>
> that's... not nearly usable or enough. Caches are relatively smart
> about things like use-once.... and they're huge. 12Mb today. You'd need
> patterns bigger than 100Mb to get even close to being reasonably
> confident that there's nothing left.
>
> > ... and IIRC my celeron testing confirmed it, if
> > I disabled L2 cache in BIOS, memtest behave differently.
> >
> > Anyway, if you can do iopl(), we may as well let you disable caches,
> > but you are right, that will need a kernel patch.
>
> and a new syscall of some sorts I suspect; "flush all caches" is a ring
> 0 operation (and you probably need to do it in an ipi anyway on all
> cpus)
>
I think that PAT support will help a lot.
How about opening/mmaping /dev/mem, and setting uncacheable attribute there.
Actually it is even possible today with MTRRs.
Regards,
Maxim Levitsky
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