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Date: Wed, 17 Sep 2014 01:46:02 -0700 From: "H. Peter Anvin" <hpa@...or.com> To: Filipe Brandenburger <filbranden@...gle.com>, Andy Lutomirski <luto@...capital.net> CC: Richard Larocque <rlarocque@...gle.com>, Ingo Molnar <mingo@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Michael Davidson <md@...gle.com>, Greg Thelen <gthelen@...gle.com>, X86 ML <x86@...nel.org>, Linux API <linux-api@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] x86/vdso: Add prctl to set per-process VDSO load On 09/16/2014 11:21 PM, Filipe Brandenburger wrote: > Hi Andy, > > On Tue, Sep 16, 2014 at 10:00 PM, Andy Lutomirski <luto@...capital.net> 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-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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