On Fri, Dec 2, 2016 at 11:24 AM, Linus Torvalds
<torva...@linux-foundation.org> wrote:
> On Fri, Dec 2, 2016 at 11:20 AM, Borislav Petkov <b...@alien8.de> wrote:
>>
>> Something like below?
>
> The optimize-nops thing needs it too, I think.
>
> Again, this will never matter in practice (even if somebody has a i486
> s till, the prefetch window size is like 16 bytes or something), but
> from a documentation standpoint it's good.
How's this?
/*
* This function forces the icache and prefetched instruction stream to
* catch up with reality in two very specific cases:
*
* a) Text was modified using one virtual address and is about to be executed
* from the same physical page at a different virtual address.
*
* b) Text was modified on a different CPU, may subsequently be
* executed on this CPU, and you want to make sure the new version
* gets executed. This generally means you're calling this in a IPI.
*
* If you're calling this for a different reason, you're probably doing
* it wrong.
*/
static inline void native_sync_core(void) { ... }
The body will do a MOV-to-CR2 followed by jmp 1f; 1:. This sequence
should be guaranteed to flush the pipeline on any real CPU. On Xen it
will do IRET-to-self.
I suppose it could be an unconditional IRET-to-self, but that's a good
deal slower and not a whole lot simpler. Although if we start doing
it right, performance won't really matter here.
--Andy
