On Thu, Mar 7, 2019 at 9:06 AM Borislav Petkov <bp@xxxxxxxxx> wrote: > > On Thu, Mar 07, 2019 at 08:53:34AM -0800, hpa@xxxxxxxxx wrote: > > If we *do*, what is the issue here? Although boot_cpu_has() isn't > > slow (it should in general be possible to reduce to one testb > > instruction followed by a conditional jump) it seems that "avoiding an > > alternatives slot" *should* be a *very* weak reason, and seems to me > > to look like papering over some other problem. > > Forget the current thread: this is simply trying to document when to use > static_cpu_has() and when to use boot_cpu_has(). I get asked about it at > least once a month. > > And then it is replacing clear slow paths using static_cpu_has() with > boot_cpu_has() because there's purely no need to patch there. And having > a RIP-relative MOV and a JMP is good enough for slow paths. > Should we maybe rename these functions? static_cpu_has() is at least reasonably obvious. But cpu_feature_enabled() is different for reasons I've never understood, and boot_cpu_has() is IMO terribly named. It's not about the boot cpu -- it's about doing the same thing but with less bloat and less performance. (And can we maybe collapse cpu_feature_enabled() and static_cpu_has() into the same function?) --Andy
