Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 15 Apr 2010 14:59:40 +0100 | From | Alan Cox <> | Subject | Re: [PATCH] Kconfig: Make config Filter access to /dev/mem default y |
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On Thu, 15 Apr 2010 15:41:53 +0200 Michal Svoboda <michal.svoboda@agents.felk.cvut.cz> wrote:
> Jiri Kosina wrote: > > Access to /dev/mem being filtered in PAT obviously applies only to x86. > > > > Architectures which don't do such filtering in their respective > > phys_mem_access_prot_allowed() still need this option. > > So why not use it for all archs uniformly? Is PAT filtering better in > some ways?
PAT is an x86 specific hardware feature. The x86 processors can set per page caching properties as with some other CPU designs. In the x86 case all references to the page must have the same cache settings so the PAT implementation has to filter /dev/mem access to avoid machine check errors.
It's not implemented as a security feature, its a side effect of the hardware requirements on that CPU range.
Alan
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