linux-kernel - Re: [patch V6 15/37] x86/entry: Change exit path of xen_failsafe

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Message-ID: <CALCETrV=qqk7ouxFTC4_Huc5xLxd1z4s6vkHX8zkfb-ez91jLA@mail.gmail.com>
Date:   Tue, 19 May 2020 13:14:13 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V6 15/37] x86/entry: Change exit path of xen_failsafe_callback

On Fri, May 15, 2020 at 5:10 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>
>
> xen_failsafe_callback is invoked from XEN for two cases:
>
>   1. Fault while reloading DS, ES, FS or GS
>   2. Fault while executing IRET
>
> #1 retries the IRET after XEN has fixed up the segments.
> #2 injects a #GP which kills the task
>
> For #1 there is no reason to go through the full exception return path
> because the tasks TIF state is still the same. So just going straight to
> the IRET path is good enough.

Seems reasonable:

Acked-by: Andy Lutomirski <luto@...nel.org>

Although a look from a Xen person might be nice too.