On 1/23/19 14:20, Jan Beulich wrote:
>>>> On 23.01.19 at 12:51, <nmant...@amazon.de> wrote:
>> --- a/xen/include/xen/nospec.h
>> +++ b/xen/include/xen/nospec.h
>> @@ -58,6 +58,21 @@ static inline unsigned long
>> array_index_mask_nospec(unsigned long index,
>> (typeof(_i)) (_i & _mask); \
>> })
>>
>> +/*
>> + * allow to insert a read memory barrier into conditionals
>> + */
>> +#ifdef CONFIG_X86
>> +static inline bool lfence_true(void) { rmb(); return true; }
>> +#else
>> +static inline bool lfence_true(void) { return true; }
>> +#endif
>> +
>> +/*
>> + * protect evaluation of conditional with respect to speculation
>> + */
>> +#define evaluate_nospec(condition) \
>> + (((condition) && lfence_true()) || !lfence_true())
> It may be just me, but I think
>
> #define evaluate_nospec(condition) \
> ((condition) ? lfence_true() : !lfence_true())
>
> would better express the two-way nature of this.
I compared the binary output of the two variants, and they are the same
(for my build environment). I'll switch to your variant, in case nobody
objects.
Best,
Norbert
>
> Jan
>
>
Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrer: Christian Schlaeger, Ralf Herbrich
Ust-ID: DE 289 237 879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
