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

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Date:   Thu, 23 Jul 2020 16:53:19 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Alex Belits <abelits@...vell.com>,
        "frederic\@kernel.org" <frederic@...nel.org>,
        "rostedt\@goodmis.org" <rostedt@...dmis.org>,
        Prasun Kapoor <pkapoor@...vell.com>,
        "mingo\@kernel.org" <mingo@...nel.org>,
        "davem\@davemloft.net" <davem@...emloft.net>,
        "linux-api\@vger.kernel.org" <linux-api@...r.kernel.org>,
        "linux-arch\@vger.kernel.org" <linux-arch@...r.kernel.org>,
        "catalin.marinas\@arm.com" <catalin.marinas@....com>,
        "will\@kernel.org" <will@...nel.org>,
        "linux-arm-kernel\@lists.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev\@vger.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v4 00/13] "Task_isolation" mode

Peter Zijlstra <peterz@...radead.org> writes:
> On Thu, Jul 23, 2020 at 03:17:04PM +0200, Thomas Gleixner wrote:
>
>>   2) Instruction synchronization
>> 
>>      Trying to do instruction synchronization delayed is a clear recipe
>>      for hard to diagnose failures. Just because it blew not up in your
>>      face does not make it correct in any way. It's broken by design and
>>      violates _all_ rules of safe instruction patching and introduces a
>>      complete trainwreck in x86 NMI processing.
>> 
>>      If you really think that this is correct, then please have at least
>>      the courtesy to come up with a detailed and precise argumentation
>>      why this is a valid approach.
>> 
>>      While writing that up you surely will find out why it is not.
>
> So delaying the sync_core() IPIs for kernel text patching _might_ be
> possible, but it very much wants to be a separate patchset and not
> something hidden inside a 'gem' like this.

I'm not saying it's impossible, but the proposed hack is definitely
beyond broken and you really don't want to be the one who has to mop up
the pieces later.

Thanks,

        tglx