lkml.org 
[lkml]   [2022]   [Apr]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] arm64: kcsan: Fix kcsan test_barrier fail and panic
On Tue, Apr 26, 2022 at 02:10:06PM +0200, Marco Elver wrote:
> On Tue, Apr 26, 2022 at 08:17AM +0000, Kefeng Wang wrote:
> > diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
> > index fd7e8fbaeef1..18863c50e9ce 100644
> > --- a/include/asm-generic/barrier.h
> > +++ b/include/asm-generic/barrier.h
> > @@ -38,6 +38,10 @@
> > #define wmb() do { kcsan_wmb(); __wmb(); } while (0)
> > #endif
> >
> > +#ifdef __dma_mb
> > +#define dma_mb() do { kcsan_mb(); __dma_mb(); } while (0)
> > +#endif
> > +
>
> So it looks like arm64 is the only arch that defines dma_mb(). By adding
> it to asm-generic, we'd almost be encouraging other architectures to add
> it, which I don't know we want.
>
> Documentation/memory-barriers.txt doesn't mention dma_mb() either - so
> perhaps dma_mb() doesn't belong in asm-generic/barrier.h, and you could
> only change arm64's definition of dma_mb() to add the kcsan_mb().
>
> Preferences? Maybe arch64 maintainers have more background on why arm64
> is an anomaly here.

Looking around, there's a single user:

[mark@lakrids:~/src/linux]% git grep -w dma_mb
arch/arm64/include/asm/barrier.h:#define dma_mb() dmb(osh)
arch/arm64/include/asm/io.h:#define __iomb() dma_mb()

[mark@lakrids:~/src/linux]% git grep -w __iomb
arch/arm64/include/asm/io.h:#define __iomb() dma_mb()
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c: __iomb();

... and that was introduced in commit:

a76a37777f2c936b ("iommu/arm-smmu-v3: Ensure queue is read after updating prod pointer")

... where it is used to ensure that prior (read and write) accesses to
memory by a CPU are ordered w.r.t. a subsequent MMIO write.

That seems like it could be a generic shape of problem (especially for
IOMMUs), even if arm64 is the only architecture with an implementation
today. From my PoV it would weem to make sense as a generic thing, and
should probably be added to Documentation/memory-barriers.txt.

Will, thoughts?

Thanks,
Mark.

\
 
 \ /
  Last update: 2022-04-26 14:52    [W:0.248 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site