On Mon, Apr 2, 2018 at 8:13 PM, Sinan Kaya <okaya@xxxxxxxxxxxxxx> wrote:
> While a barrier is present in writeX() function before the register write,
> a similar barrier is missing in the readX() function after the register
> read. This could allow memory accesses following readX() to observe
> stale data.
>
> Signed-off-by: Sinan Kaya <okaya@xxxxxxxxxxxxxx>
> Reported-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> arch/mips/include/asm/io.h | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/mips/include/asm/io.h b/arch/mips/include/asm/io.h
> index 0cbf3af..7f9068d 100644
> --- a/arch/mips/include/asm/io.h
> +++ b/arch/mips/include/asm/io.h
> @@ -377,6 +377,7 @@ static inline type pfx##read##bwlq(const volatile void __iomem *mem) \
> BUG(); \
> } \
> \
> + war_io_reorder_wmb(); \
> return pfx##ioswab##bwlq(__mem, __val); \
> }
I'm not sure if this is the right barrier: what we want here is a read
barrier to
prevent any following memory access from being prefetched ahead of the readl(),
so I would have expected a kind of rmb() rather than wmb().
The barrier you used here is defined as
#if defined(CONFIG_CPU_CAVIUM_OCTEON) || defined(CONFIG_LOONGSON3_ENHANCEMENT)
#define war_io_reorder_wmb() wmb()
#else
#define war_io_reorder_wmb() do { } while (0)
#endif
which appears to list the particular CPUs that have a reordering
write buffer. That may not be the same set of CPUs that have the
capability to do out-of-order loads.
Arnd
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