On 4/3/2018 3:21 AM, Arnd Bergmann wrote:
> 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().
>
That's true. There was too much macro-ism in the code. I was thinking war_io_reorder_wmb()
to be a mb() under the hood. I'll fix and post an update.
> 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
>
--
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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