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SubjectRe: [PATCH v2 05/20] ARM: LPAE: Introduce L_PTE_NOEXEC and L_PTE_NOWRITE
On Tue, Nov 16, 2010 at 03:18:03PM +0000, Catalin Marinas wrote:
> On 15 November 2010 18:30, Russell King - ARM Linux
> <linux@arm.linux.org.uk> wrote:
> > Let's not make this more complicated than it has to be.  If we need the
> > inverse of WRITE and EXEC, then that's what we should change everyone to,
> > not invent a new system to work along side the old system.
> This adds an additional instruction in set_pte_ext, unless you can
> write the bit checking in a better way:

It actually results in the same number of instructions. From memory:

ARMv3-ARMv5:
- eor r3, r1, #L_PTE_PRESENT | L_PTE_YOUNG | L_PTE_WRITE | L_PTE_DIRTY
- tst r3, #L_PTE_WRITE | L_PTE_DIRTY @ write and dirty?
- orreq r2, r2, #PTE_SMALL_AP_UNO_SRW
+ eor r3, r1, #L_PTE_PRESENT | L_PTE_YOUNG | L_PTE_DIRTY
+ tst r3, #L_PTE_RDONLY | L_PTE_DIRTY @ write and dirty?
+ orreq r2, r2, #PTE_SMALL_AP_UNO_SRW
and for ARMv6+:

- tst r1, #L_PTE_WRITE
- tstne r1, #L_PTE_DIRTY
- orreq r3, r3, #PTE_EXT_APX
+ eor r1, r1, #L_PTE_DIRTY
+ tst r1, #L_PTE_RDONLY | L_PTE_DIRTY
+ orrne r3, r3, #PTE_EXT_APX
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