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SubjectRe: [PATCH 20/30] microblaze_mmu_v1: uaccess MMU update
Arnd Bergmann wrote:
> On Wednesday 29 April 2009, Michal Simek wrote:
>>> The above is just the nommu variant. For mmu, you need to
>>> have exception handling in __clear_user to take care of the
>>> case where the address is part of the user mapping (access_ok)
>>> but not currently mapped.
>> Is it possible to do it for noMMU kernel too? I mean current MMU
>> implementation of __clear_user in asm is faster than call memset
>> for noMMU. I think I can use MMU implementation for noMMU too.
>> Add two words to __ex_table just extend size of one section but
>> not too much and won't be used for noMMU.
>
> Well, you can probably do something like this:
>
> #ifdef CONFIG_MMU
> #define __FIXUP_SECTION ".section .fixup,\"ax\"\n"
> #define __EX_TABLE_SECTION ".section __ex_table,\"a\"\n"
> #else
> #define __FIXUP_SECTION ".section .discard,\"ax\"\n"
> #define __EX_TABLE_SECTION ".section .discard,\"a\"\n"
> #endif
>
> +#define __get_user_asm(insn, __gu_ptr, __gu_val, __gu_err) \
> +({ \
> + __asm__ __volatile__ ( \
> + "1:" insn " %1, %2, r0; \n" \
> + " addk %0, r0, r0; \n" \
> + "2: \n" \
> + __FIXUP_SECTION \
> + "3: brid 2b \n" \
> + " addik %0, r0, %3 \n" \
> + ".previous \n" \
> + __EX_TABLE_SECTION \
> + ".word 1b,3b \n" \
> + ".previous \n" \
> + : "=r"(__gu_err), "=r"(__gu_val) \
> + : "r"(__gu_ptr), "i"(-EFAULT) \
> + ); \
> +})
>
> This should simply throw away all the fixups if you list the .discard
> section in vmlinux.lds.S under '/DISCARD/:', so you have no
> overhead at all.

ok. I'll try it.

I look at user_bad macros.

#define __get_user_bad() (bad_user_access_length(), (-EFAULT))

For powerpc I found these tree references. Where is the __get_user_bad definition?
arch/powerpc/include/asm/uaccess.h:216:extern long __get_user_bad(void);
arch/powerpc/include/asm/uaccess.h:263: (x) = __get_user_bad(); \
arch/powerpc/include/asm/uaccess.h:269: default: (x) = __get_user_bad(); \

Michal


>
> Arnd <><


--
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854


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