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    Subject[PATCH 5.18 273/339] x86/cpu: Elide KCSAN for cpu_has() and friends
    Date
    From: Peter Zijlstra <peterz@infradead.org>

    [ Upstream commit a6a5eb269f6f3a2fe392f725a8d9052190c731e2 ]

    As x86 uses the <asm-generic/bitops/instrumented-*.h> headers, the
    regular forms of all bitops are instrumented with explicit calls to
    KASAN and KCSAN checks. As these are explicit calls, these are not
    suppressed by the noinstr function attribute.

    This can result in calls to those check functions in noinstr code, which
    objtool warns about:

    vmlinux.o: warning: objtool: enter_from_user_mode+0x24: call to __kcsan_check_access() leaves .noinstr.text section
    vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0x28: call to __kcsan_check_access() leaves .noinstr.text section
    vmlinux.o: warning: objtool: syscall_enter_from_user_mode_prepare+0x24: call to __kcsan_check_access() leaves .noinstr.text section
    vmlinux.o: warning: objtool: irqentry_enter_from_user_mode+0x24: call to __kcsan_check_access() leaves .noinstr.text section

    Prevent this by using the arch_*() bitops, which are the underlying
    bitops without explciit instrumentation.

    [null: Changelog]
    Reported-by: kernel test robot <lkp@intel.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Link: https://lkml.kernel.org/r/20220502111216.290518605@infradead.org
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/include/asm/cpufeature.h | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
    index 1261842d006c..49a3b122279e 100644
    --- a/arch/x86/include/asm/cpufeature.h
    +++ b/arch/x86/include/asm/cpufeature.h
    @@ -51,7 +51,7 @@ extern const char * const x86_power_flags[32];
    extern const char * const x86_bug_flags[NBUGINTS*32];

    #define test_cpu_cap(c, bit) \
    - test_bit(bit, (unsigned long *)((c)->x86_capability))
    + arch_test_bit(bit, (unsigned long *)((c)->x86_capability))

    /*
    * There are 32 bits/features in each mask word. The high bits
    --
    2.35.1


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