Re: [Xen-devel] [PATCH 4/4] xen/x86: Correct mandatory and SMP barrier definitions

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/12/16 10:11, Juergen Gross wrote:
> On 05/12/16 11:05, Andrew Cooper wrote:
>> Barriers are a complicated topic, a common source of confusion in submitted
>> code, and their incorrect use is a common cause of bugs.  It *really* doesn't
>> help when Xen's API is the same as Linux, but its ABI different.
>>
>> Bring the two back in line, so programmers stand a chance of actually getting
>> their use correct.
>>
>> As Xen has no current need for mandatory barriers, leave them commented out 
>> to
>> avoid accidential misue.
>>
>> No functional change.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> ---
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>> ---
>>  xen/include/asm-x86/system.h        | 31 +++++++++++++++++++++++--------
>>  xen/include/asm-x86/x86_64/system.h |  3 ---
>>  2 files changed, 23 insertions(+), 11 deletions(-)
>>
>> diff --git a/xen/include/asm-x86/system.h b/xen/include/asm-x86/system.h
>> index 9cb6fd7..9cd401a 100644
>> --- a/xen/include/asm-x86/system.h
>> +++ b/xen/include/asm-x86/system.h
>> @@ -164,23 +164,38 @@ static always_inline unsigned long __xadd(
>>      ((typeof(*(ptr)))__xadd(ptr, (typeof(*(ptr)))(v), sizeof(*(ptr))))
>>  
>>  /*
>> + * Mandatory barriers, for the ordering of reads and writes with MMIO 
>> devices
>> + * mapped with reduced cacheability.
>> + *
>> + * Xen has no such device drivers, and therefore no need for mandatory
>> + * barriers.  These these are hidden to avoid their misuse; If a future need
> Duplicate "these".

Fixed, thanks.

~Andrew

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