Question about ARM set_pte_ext

Question about ARM set_pte_ext

[Sasha Sirotkin]

I'm still trying to understand the peculiarities of ARMv5 memory 
management...

I have a question about ARM set_pte_ext or armv3_set_pte_ext to be more 
specific.
In the following lines

    tst    r3, #L_PTE_USER            @ user?
    orrne    r2, r2, #PTE_SMALL_AP_URO_SRW

We are testing for L_PTE_USER not being set. Why not?

Another question is about S & R bits of CP15 register 1, which on ARMv5 
are used to control memory access in combination with AP bits. As 
changing S & R bits requires to reset the MMU, basically it is 
impossible to use them, if I wanted to configured a certain page to be, 
for instance, read-only for both kernel and user modes?

Thanks.

Question about ARM set_pte_ext

[Dmytro Milinevskyy]

Hello, Sasha.
You are misunderstanding ARM ASM.
tst operation is updating flags on Rn & Rd, so if L_PTE_USER was set
in r3, then Z flag is not set and orrne operation will be performed,
because {ne} conditional states to execute operation if Z was not set.
So if r3 has L_PTE_USER then r2 will be orred with
PTE_SMALL_AP_URO_SRW

-- Dima

On Sat, Apr 17, 2010 at 10:44 AM, Sasha Sirotkin
<buildroot@browserseal.com> wrote:
> I'm still trying to understand the peculiarities of ARMv5 memory
> management...
>
> I have a question about ARM set_pte_ext or armv3_set_pte_ext to be more
> specific.
> In the following lines
>
> ? tst ? ?r3, #L_PTE_USER ? ? ? ? ? ?@ user?
> ? orrne ? ?r2, r2, #PTE_SMALL_AP_URO_SRW
>
> We are testing for L_PTE_USER not being set. Why not?
>
> Another question is about S & R bits of CP15 register 1, which on ARMv5 are
> used to control memory access in combination with AP bits. As changing S & R
> bits requires to reset the MMU, basically it is impossible to use them, if I
> wanted to configured a certain page to be, for instance, read-only for both
> kernel and user modes?
>
> Thanks.
>
>
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> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>