x86/cpu: Elide KCSAN for cpu_has() and friends
authorPeter Zijlstra <peterz@infradead.org>
Mon, 2 May 2022 10:15:23 +0000 (12:15 +0200)
committerPeter Zijlstra <peterz@infradead.org>
Fri, 27 May 2022 10:34:43 +0000 (12:34 +0200)
commita6a5eb269f6f3a2fe392f725a8d9052190c731e2
treeeb976f890bfed9fcc3231423542da222b3dc58df
parent385bd430c011a8cb8278e61c32d602d11e06f414
x86/cpu: Elide KCSAN for cpu_has() and friends

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
arch/x86/include/asm/cpufeature.h