linux-kernel - Re: [patch V4 part 1 27/36] arm64: Prepare arch_nmi

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Date:   Fri, 15 May 2020 23:31:13 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        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>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [patch V4 part 1 27/36] arm64: Prepare arch_nmi_enter() for
 recursion

On Fri, May 15, 2020 at 11:29:13PM +0200, Thomas Gleixner wrote:
> Thomas Gleixner <tglx@...utronix.de> writes:
> 
> > From: Frederic Weisbecker <frederic@...nel.org>
> 
> This changelog was very empty. Here is what Peter provided:
> 
>  When using nmi_enter() recursively, arch_nmi_enter() must also be recursion
>  safe. In particular, it must be ensured that HCR_TGE is always set while in
>  NMI context when in HYP mode, and be restored to it's former state when
>  done.
> 
>  The current code fails this when interleaved wrong. Notably it overwrites
>  the original hcr state on nesting.
> 
>  Introduce a nesting counter to make sure to store the original value.

Nice!

Thanks.