On Fri, 2018-08-31 at 07:47 -0700, Dave Hansen wrote:
> On 08/31/2018 07:33 AM, Yu-cheng Yu wrote:
> >
> > Please use the form:
> >
> > pte_t new_pte, pte = READ_ONCE(*ptep);
> > do {
> > new_pte = /* ... */;
> > } while (!try_cmpxchg(ptep, &pte, new_pte);
> It's probably also worth doing some testing to see if you can detect
> the
> cost of the cmpxchg. It's definitely more than the old code.
>
> A loop that does mprotect(PROT_READ) followed by
> mprotect(PROT_READ|PROT_WRITE) should do it.
I created the test,
https://github.com/yyu168/cet-smoke-test/blob/quick/quick/mprotect_ben
ch.c
then realized this won't work.
To trigger a race in ptep_set_wrprotect(), we need to fork from one of
three pthread siblings.
Or do we measure only how much this affects fork?
If there is no racing, the effect should be minimal.
Yu-cheng
