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From:   Thomas Gleixner <tglx@linutronix.de>
To:     LKML <linux-kernel@vger.kernel.org>
Cc:     x86@kernel.org, "Paul E. McKenney" <paulmck@kernel.org>,
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Subject: Re: [patch V4 part 1 27/36] arm64: Prepare arch_nmi_enter() for recursion
In-Reply-To: <20200505134100.771491291@linutronix.de>
References: <20200505131602.633487962@linutronix.de> <20200505134100.771491291@linutronix.de>
Date:   Fri, 15 May 2020 23:29:13 +0200
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Thomas Gleixner <tglx@linutronix.de> writes:

> From: Frederic Weisbecker <frederic@kernel.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.