Hi Marc, On Wed, Aug 30, 2017 at 09:46:26AM +0100, Marc Zyngier wrote: [...] > >> This is completely busted: > >> > >> - You are only addressing the kernel side, and ignore userspace (which > >> is just as broken as the kernel). > > > > Thanks for quick reviewing. > > > > Yeah, I remembered there have some code directly reads arch timer > > virtual counter from userspace. But can you remind for userspace > > broken issue, is the code in libc or vdso? > > You're missing the point. The virtual counter is freely available to > userspace to play with (this is a de-facto ABI). Since it can return bad > values, it needs to be trapped to be correctly emulated (together with > cntfrq_el0), and the VDSO disabled. > > > Here I have another question is: after applied the whole workaround > > infrastructure, can it also fix userspace broken issue? > > Yup. That's why I ended-up with a 18 patches series, and not just this > single one. Trust me, I'm lazy. There is nothing I hate more than doing > useless work. Thanks for detailed explaination. Now it's much clear for me. > >> - You lie in the description of the option (this is in no way dynamic, > >> since you didn't backport the whole workaround infrastructure). > > > > I should fix it. > > > >> So I'm afraid I'm NAKing this. Please refrain from blindly backporting > >> random patches. fa8d815fac96e7c9 only makes sense in the context of the > >> whole series, and on its own gives you a very false sense of having > >> properly addressed it. > > > > IIUC, at least fa8d815fac96e7c9 can fix issue in kernel side, such like > > for sched_clock() roll back issue [1]. > > What's the point of fixing the kernel if userspace is just as likely to > fail? Understand now. > > So for this issue, are you suggesting we need backport whole workaround > > infrastructure onto kernel 4.4 and 4.9? Many ARM devices are working > > with these two kernels. > > Then these systems are completely broken if they use a Cortex-A73. > Either they run mainline (which will be just fine), or they get a fully > backported workaround infrastructure. Yeah, we should do right thing. Have ARM kernel team ported this patch series (or is in planning)? I also will check with Linaro kernel team as well, I just want to avoid duplicate efforts if these patches have been back ported. Otherwise, I will backport the patch series. Thanks, Leo Yan