linux-kernel - Re: [PATCH v4 00/13] "Task

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Message-ID: <20200723154933.GB709@worktop.programming.kicks-ass.net>
Date:   Thu, 23 Jul 2020 17:49:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alex Belits <abelits@...vell.com>
Cc:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "frederic@...nel.org" <frederic@...nel.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        Prasun Kapoor <pkapoor@...vell.com>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will@...nel.org" <will@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v4 00/13] "Task_isolation" mode

On Thu, Jul 23, 2020 at 03:18:42PM +0000, Alex Belits wrote:
> On Thu, 2020-07-23 at 15:17 +0200, Thomas Gleixner wrote:
> > 
> > Without going into details of the individual patches, let me give you a
> > high level view of this series:
> > 
> >   1) Entry code handling:
> > 
> >      That's completely broken vs. the careful ordering and instrumentation
> >      protection of the entry code. You can't just slap stuff randomly
> >      into places which you think are safe w/o actually trying to understand
> >      why this code is ordered in the way it is.
> > 
> >      This clearly was never built and tested with any of the relevant
> >      debug options enabled. Both build and boot would have told you.
> 
> This is intended to avoid a race condition when entry or exit from isolation
> happens at the same time as an event that requires synchronization. The idea
> is, it is possible to insulate the core from all events while it is running
> isolated task in userspace, it will receive those calls normally after
> breaking isolation and entering kernel, and it will synchronize itself on
> kernel entry.

'What does noinstr mean? and why do we have it" -- don't dare touch the
entry code until you can answer that.