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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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