Messages in this thread | | | Date | Tue, 26 Apr 2022 13:50:39 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH] arm64: kcsan: Fix kcsan test_barrier fail and panic |
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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.
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