Re: [PATCH v4 2/2] arm64: kcsan: Support detecting more missing memory barriers

[Kefeng Wang]

Hi Will and Catalin, kindly ping...

On 2022/5/23 22:16, Mark Rutland wrote:
> On Mon, May 23, 2022 at 07:31:26PM +0800, Kefeng Wang wrote:
> > As "kcsan: Support detecting a subset of missing memory barriers"[1]
> > introduced KCSAN_STRICT/KCSAN_WEAK_MEMORY which make kcsan detects
> > more missing memory barrier, but arm64 don't have KCSAN instrumentation
> > for barriers, so the new selftest test_barrier() and test cases for
> > memory barrier instrumentation in kcsan_test module will fail, even
> > panic on selftest.
> >
> > Let's prefix all barriers with __ on arm64, as asm-generic/barriers.h
> > defined the final instrumented version of these barriers, which will
> > fix the above issues.
> >
> > Note, barrier instrumentation that can be disabled via __no_kcsan with
> > appropriate compiler-support (and not just with objtool help), see
> > commit bd3d5bd1a0ad ("kcsan: Support WEAK_MEMORY with Clang where no
> > objtool support exists"), it adds disable_sanitizer_instrumentation to
> > __no_kcsan attribute which will remove all sanitizer instrumentation fully
> > (with Clang 14.0). Meanwhile, GCC does the same thing with no_sanitize.
> >
> > [1] https://lore.kernel.org/linux-mm/20211130114433.2580590-1-elver@xxxxxxxxxx/
> >
> > Acked-by: Marco Elver <elver@xxxxxxxxxx>
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> Having built this with GCC 12.1.0 and LLVM 14.0.0, I think this patch itself
> doesn't introduce any new problems, and logically makes sense. With that in
> mind:
>
>    Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
>
> As an aside, having scanned the resulting vmlinux with objdump, there are
> plenty of latent issues where we get KCSAN instrumentation where we don't want
> it (e.g. early/late in arm64's entry-common.o). The bulk of those are due to
> missing `nonistr` or `__always_inline`, which we'll need to fix up.
>
> Thanks,
> Mark.
>
> > ---
> >   arch/arm64/include/asm/barrier.h | 12 ++++++------
> >   1 file changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
> > index 9f3e2c3d2ca0..2cfc4245d2e2 100644
> > --- a/arch/arm64/include/asm/barrier.h
> > +++ b/arch/arm64/include/asm/barrier.h
> > @@ -50,13 +50,13 @@
> >   #define pmr_sync()	do {} while (0)
> >   #endif
> >   
> > -#define mb()		dsb(sy)
> > -#define rmb()		dsb(ld)
> > -#define wmb()		dsb(st)
> > +#define __mb()		dsb(sy)
> > +#define __rmb()		dsb(ld)
> > +#define __wmb()		dsb(st)
> >   
> > -#define dma_mb()	dmb(osh)
> > -#define dma_rmb()	dmb(oshld)
> > -#define dma_wmb()	dmb(oshst)
> > +#define __dma_mb()	dmb(osh)
> > +#define __dma_rmb()	dmb(oshld)
> > +#define __dma_wmb()	dmb(oshst)
> >   
> >   #define io_stop_wc()	dgh()
> >   
> > --
> > 2.35.3
> .