On 09/16/2014 11:21 PM, Filipe Brandenburger wrote: > Hi Andy, > > On Tue, Sep 16, 2014 at 10:00 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >> I think that the patch should instead tweak the vvar mapping to tell >> the vdso not to use rdtsc. It should be based on this: > > I've been working on this approach which extends the vvar from 2 to 3 > pages. The third page would initially be mapped to a zero page but > then through a prctl a task could replace it with a real page that > could then be inherited through fork and exec. > > That would make it possible to have per-task vvar contents. > > We could use some of those values as flags to indicate whether vdso > routines may use RDTSC or not. > > In the future, we're planning to also use that to store clock offsets > so that we can ensure CLOCK_MONOTONIC works after CRIU migration > without having to turn off the VDSO or have to always fallback to full > syscalls on every case. > > Do you think that would be a reasonable way to accomplish that? > Why would we need/want per process vvar contents? It seems better to have the code swapped out. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
