On Fri, Mar 22, 2019 at 12:04:55PM -0700, Stephane Eranian wrote: > On Thu, Mar 21, 2019 at 10:51 AM Thomas Gleixner <t...@linutronix.de> wrote: > > > > On Thu, 21 Mar 2019, Stephane Eranian wrote: > > > On Thu, Mar 21, 2019 at 9:45 AM Thomas Gleixner <t...@linutronix.de> > > > wrote: > > > > > > > > On Thu, 21 Mar 2019, Peter Zijlstra wrote: > > > > > Subject: perf/x86/intel: Initialize TFA MSR > > > > > > > > > > Stephane reported that we don't initialize the TFA MSR, which could > > > > > lead > > > > > to trouble if the RESET value is not 0 or on kexec. > > > > > > > > That sentence doesn't parse. > > > > > > > > Stephane reported that the TFA MSR is not initialized by the kernel, > > > > but > > > > the TFA bit could set by firmware or as a leftover from a kexec, which > > > > makes the state inconsistent. > > > > > > > Correct. This is what I meant. > > > The issue is what does the kernel guarantee when it boots? > > > > > > I see: > > > static bool allow_tsx_force_abort = true; > > > > > > Therefore you must ensure the MSR is set to reflect that state on boot. > > > So you have to force it to that value to be in sync which is what your > > > new patch is doing. > > > > The initial state should be that the MSR TFA bit is 0. The software state > > is a different beast. > > > > allow_tsx_force_abort > > > > false Do not set MSR TFA bit (Make TSX work with PMC3) and > > exclude PMC3 from being used. > > > > true Set the MSR TFA bit when PMC3 is used by perf, > > clear it > > when PMC3 is not longer in use. > > > I would expect this description to be included in the source code where the > allow_tsx_force_abort variable is defined
That part is easy I suppose. > and somewhere in the kernel Documentation because it is not trivial to > understand what the control actually does and the guarantees you have > when you toggle it. But here we seem to be sorely lacking, that is, there is no sysfs/perf documentation at all. In any case, feel free to send a patch :-)
