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SubjectRe: Turn CONFIG_STRICT_DEVMEM in sysctl dev.mem.restricted
On Sun, 16 Nov 2008 16:56:09 +0100
Bernhard Walle <> wrote:

> > > While the original submission of CONFIG_STRICT_DEVMEM mentions
> > > that the option has been in RHEL and Fedora for 4 years without
> > > problems, that's only a half of the story. The truth is that at
> > > least RHEL has /dev/crash exactly to circumvent that /dev/mem
> > > restriction. Don't tell me that this is better than having that
> > > sysctl entry. ;-)
> >
> > I assume /dev/crash is read only
> I don't know. But if that matters, why can't we make /dev/mem
> write-only for certain areas and read-only for the rest ...?
> > You either want this at compile time or you don't want it at all.
> Why? You don't write something about my arguments (as Alan does, even
> though I disagree), you only write that you "nak" it.

It's very simple: if you want the strict form you really want the
strict form, not some half "oh but it's one line to turn off" form.

(Note: your usecase is in trouble in general already with PAT used by
modern video drivers: the requirement is that all mappings of the same
physical page are mapped with the same cachability semantics. mmaping
random parts of physical real memory via /dev/mem makes that a way too
complex issue and will likely turn the crash utility in what it's name
says ;-)

Arjan van de Ven Intel Open Source Technology Centre
For development, discussion and tips for power savings,

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