Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 10 Aug 2023 22:36:40 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Borislav Petkov <bp@alien8.de>,
        Ashok Raj <ashok.raj@intel.com>,
        Arjan van de Ven <arjan@linux.intel.com>
Subject: Re: [patch 26/30] x86/microcode: Protect against instrumentation
Message-ID: <20230810203640.GE212435@hirez.programming.kicks-ass.net>
References: <20230810153317.850017756@linutronix.de>
 <20230810160806.448579267@linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230810160806.448579267@linutronix.de>
Precedence: bulk

On Thu, Aug 10, 2023 at 08:38:04PM +0200, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> The wait for control loop in which the siblings are waiting for the
> microcode update on the primary thread must be protected against
> instrumentation as instrumentation can end up in #INT3, #DB or #PF, which
> then returns with IRET. That IRET reenables NMI which is the opposite of
> what the NMI rendezvouz is trying to achieve.

asm_exc_nmi will re-enable NMIs when DEBUG_ENTRY before we reach C.
Late loading had better depend on !DEBUG_ENTRY.