On 2/4/19 10:18 PM, Borislav Petkov wrote: > On Mon, Feb 04, 2019 at 03:24:23PM -0800, Dave Hansen wrote: >> Actually, there's one part of all this that I forgot. Will split lock >> detection be enumerated _widely_? > > You never know what users will do. The moment it gets out, it better be > designed properly, along with the chicken bits.
Sure. I think this was just the simplest implementation we could come up with. There was more complexity before, and Thomas suggested stripping it back to the bare-bones like we have here. >> IOW, will my laptop in 5 years enumerate support for it? > > Don't tell me this is going to be another MPX fiasco :-\ > > Or is this something along the lines of "let's see whether it takes off > and if yes, we'll commit to it or otherwise remove it and not even waste > a CPUID leaf"? "Is Intel serious enough to put in a CPUID leaf" is a pretty good litmus test INMHO. I think it's one of the reasons that Thomas said he would consider this if Intel was willing to go to the trouble of adding proper enumeration. >> If so, we surely don't want to enable this everyhwhere: it will break >> old apps. Doesn't that mean that we need both feature detection and >> another separate bit for folks to opt-in? > > Well, if it breaks old apps, it probably needs to be opt-in anyway. Yes, this was my assumption. > And for that you don't need setcpuid either - you simply boot with > "split_lock_ac" or whatever and the kernel pokes that MSR_TEST_CTL or > whatever else it needs to detect in hw for split lock and sets the > X86_FEATURE bits if detection is successful. That's actually what we did in the last set. Anyway... There are a few branches of this discussion. Let's wait for Fenghua to tell us how universal this feature is and if family/model/stepping detection will work.
