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

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Message-ID: <873680evkm.fsf@nanos.tec.linutronix.de>
Date:   Fri, 15 May 2020 23:29:13 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     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>,
        "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

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.