linux-kernel - Re: [Uclinux-dist-devel] [PATCH v2] NOMMU: add support for Memory Protection Units (MPU)

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Message-ID: <3751.1247660742@redhat.com>
Date:	Wed, 15 Jul 2009 13:25:42 +0100
From:	David Howells <dhowells@...hat.com>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	dhowells@...hat.com, Bernd Schmidt <bernds_cb1@...nline.de>,
	uclinux-dist-devel@...ckfin.uclinux.org,
	linux-kernel@...r.kernel.org
Subject: Re: [Uclinux-dist-devel] [PATCH v2] NOMMU: add support for Memory Protection Units (MPU)

Mike Frysinger <vapier.adi@...il.com> wrote:

> yes, you can see page_rwx_mask in our mmu.h's mm_context_t.  this is
> what the protect_page/update_protections operate on.  we have a global
> current_rwx_mask that gets updated during context changes and the CPLB
> miss handler uses that to keep things simple.

Interesting.

Since FRV does not really allow separate execute permissions (it has a very
few separate static I and D protection/mapping registers and a shared TLB), I
could do it with just pairs of bits.

Also, how do you deal with mappable devices that lie outside of RAM?  I'm
guessing from the code that you don't cover those with the bitmap, but rather
just grant userspace RW access.

David
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