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    Subject[PATCH] x86-64: modify copy_user_generic() alternatives mechanism
    In order to avoid unnecessary chains of branches, rather than
    implementing copy_user_generic() as a function consisting of just a
    single (possibly patched) branch, instead properly deal with patching
    call instructions in the alternative instructions framework, and
    move the patching into the callers.

    As a follow-on, one could also introduce something like
    __EXPORT_SYMBOL_ALT() to avoid patching call sites in modules.

    Signed-off-by: Jan Beulich <jbeulich@novell.com>
    Cc: Nick Piggin <npiggin@suse.de>

    ---
    arch/x86/include/asm/alternative.h | 7 ++++++-
    arch/x86/include/asm/uaccess_64.h | 21 ++++++++++++++++++++-
    arch/x86/kernel/alternative.c | 4 +++-
    arch/x86/kernel/x8664_ksyms_64.c | 3 ++-
    arch/x86/lib/copy_user_64.S | 6 ------
    5 files changed, 31 insertions(+), 10 deletions(-)

    --- linux-2.6.33-rc1/arch/x86/include/asm/alternative.h 2009-12-18 16:16:12.000000000 +0100
    +++ 2.6.33-rc1-x86_64-copy_user_generic-alternative/arch/x86/include/asm/alternative.h 2009-12-04 12:19:20.000000000 +0100
    @@ -125,11 +125,16 @@ static inline void alternatives_smp_swit
    asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) \
    : output : "i" (0), ## input)

    +/* Like alternative_io, but for replacing a direct call with another one. */
    +#define alternative_call(oldfunc, newfunc, feature, output, input...) \
    + asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
    + : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
    +
    /*
    * use this macro(s) if you need more than one output parameter
    * in alternative_io
    */
    -#define ASM_OUTPUT2(a, b) a, b
    +#define ASM_OUTPUT2(a...) a

    struct paravirt_patch_site;
    #ifdef CONFIG_PARAVIRT
    --- linux-2.6.33-rc1/arch/x86/include/asm/uaccess_64.h 2009-12-18 16:16:12.000000000 +0100
    +++ 2.6.33-rc1-x86_64-copy_user_generic-alternative/arch/x86/include/asm/uaccess_64.h 2009-12-04 12:19:20.000000000 +0100
    @@ -8,6 +8,8 @@
    #include <linux/errno.h>
    #include <linux/prefetch.h>
    #include <linux/lockdep.h>
    +#include <asm/alternative.h>
    +#include <asm/cpufeature.h>
    #include <asm/page.h>

    /*
    @@ -16,7 +18,24 @@

    /* Handles exceptions in both to and from, but doesn't do access_ok */
    __must_check unsigned long
    -copy_user_generic(void *to, const void *from, unsigned len);
    +copy_user_generic_string(void *to, const void *from, unsigned len);
    +__must_check unsigned long
    +copy_user_generic_unrolled(void *to, const void *from, unsigned len);
    +
    +static __always_inline __must_check unsigned long
    +copy_user_generic(void *to, const void *from, unsigned len)
    +{
    + unsigned ret;
    +
    + alternative_call(copy_user_generic_unrolled,
    + copy_user_generic_string,
    + X86_FEATURE_REP_GOOD,
    + ASM_OUTPUT2("=a" (ret), "=D" (to), "=S" (from),
    + "=d" (len)),
    + "1" (to), "2" (from), "3" (len)
    + : "memory", "rcx", "r8", "r9", "r10", "r11");
    + return ret;
    +}

    __must_check unsigned long
    _copy_to_user(void __user *to, const void *from, unsigned len);
    --- linux-2.6.33-rc1/arch/x86/kernel/alternative.c 2009-12-03 04:51:21.000000000 +0100
    +++ 2.6.33-rc1-x86_64-copy_user_generic-alternative/arch/x86/kernel/alternative.c 2009-12-04 12:19:20.000000000 +0100
    @@ -205,7 +205,7 @@ void __init_or_module apply_alternatives
    struct alt_instr *end)
    {
    struct alt_instr *a;
    - char insnbuf[MAX_PATCH_LEN];
    + u8 insnbuf[MAX_PATCH_LEN];

    DPRINTK("%s: alt table %p -> %p\n", __func__, start, end);
    for (a = start; a < end; a++) {
    @@ -223,6 +223,8 @@ void __init_or_module apply_alternatives
    }
    #endif
    memcpy(insnbuf, a->replacement, a->replacementlen);
    + if (*insnbuf == 0xe8 && a->replacementlen == 5)
    + *(s32 *)(insnbuf + 1) += a->replacement - a->instr;
    add_nops(insnbuf + a->replacementlen,
    a->instrlen - a->replacementlen);
    text_poke_early(instr, insnbuf, a->instrlen);
    --- linux-2.6.33-rc1/arch/x86/kernel/x8664_ksyms_64.c 2009-12-18 16:16:13.000000000 +0100
    +++ 2.6.33-rc1-x86_64-copy_user_generic-alternative/arch/x86/kernel/x8664_ksyms_64.c 2009-12-04 12:19:20.000000000 +0100
    @@ -26,7 +26,8 @@ EXPORT_SYMBOL(__put_user_2);
    EXPORT_SYMBOL(__put_user_4);
    EXPORT_SYMBOL(__put_user_8);

    -EXPORT_SYMBOL(copy_user_generic);
    +EXPORT_SYMBOL(copy_user_generic_string);
    +EXPORT_SYMBOL(copy_user_generic_unrolled);
    EXPORT_SYMBOL(__copy_user_nocache);
    EXPORT_SYMBOL(_copy_from_user);
    EXPORT_SYMBOL(_copy_to_user);
    --- linux-2.6.33-rc1/arch/x86/lib/copy_user_64.S 2009-12-18 16:16:13.000000000 +0100
    +++ 2.6.33-rc1-x86_64-copy_user_generic-alternative/arch/x86/lib/copy_user_64.S 2009-12-04 12:19:20.000000000 +0100
    @@ -90,12 +90,6 @@ ENTRY(_copy_from_user)
    CFI_ENDPROC
    ENDPROC(_copy_from_user)

    -ENTRY(copy_user_generic)
    - CFI_STARTPROC
    - ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,copy_user_generic_unrolled,copy_user_generic_string
    - CFI_ENDPROC
    -ENDPROC(copy_user_generic)
    -
    .section .fixup,"ax"
    /* must zero dest */
    ENTRY(bad_from_user)



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