On 20/12/2019 14:55, Jan Beulich wrote: > On 20.12.2019 15:51, Andrew Cooper wrote: >> On 20/12/2019 14:20, Jan Beulich wrote: >>> get_page_light()'s use of cmpxchg() is a full barrier already anyway. >>> >>> Signed-off-by: Jan Beulich <jbeul...@suse.com> >> While true, is this actually a clever change to make? >> >> The implementation of get_page_light() could plausibly change and no >> longer be a full barrier, introducing a vulnerability here. OTOH, >> smp_wmb() is free. > It's free at the CPU level, but not at the compiler one (where > it still is a barrier). I also don't think get_page_light() > could change as drastically as losing its LOCK-ed operation, > or if it did the author (and reviewer) would be well advised > to at least briefly audit use sites (one of the reasons I'm > leaving a comment).
The comment should be at get_page_light() then, saying "some callers depend on this function being a full memory barrier", which will be far more obvious for anyone who changes the behaviour. With an adjustment along those lines, Acked-by: Andrew Cooper <andrew.coop...@citrix.com> _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
