linux-kernel - Re: [patch 6/6] x86/smp: Put CPUs into INIT on shutdown if possible

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Message-ID: <ZHupKtSqj1LC911k@a4bf019067fa.jf.intel.com>
Date:   Sat, 3 Jun 2023 13:57:14 -0700
From:   Ashok Raj <ashok.raj@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     LKML <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        Ashok Raj <ashok.raj@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Tony Luck" <tony.luck@...el.com>,
        Arjan van de Veen <arjan@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [patch 6/6] x86/smp: Put CPUs into INIT on shutdown if possible

On Sat, Jun 03, 2023 at 10:07:04PM +0200, Thomas Gleixner wrote:
> Parking CPUs in a HLT loop is not completely safe vs. kexec() as HLT can
> resume execution due to NMI, SMI and MCE, which has the same issue as the
> MWAIT loop.
> 
> Kicking the secondary CPUs into INIT makes this safe against NMI and SMI.
> 
> A broadcast MCE will take the machine down, but a broadcast MCE which makes
> HLT resume and execute overwritten text, pagetables or data will end up in
> a disaster too.
> 
> So chose the lesser of two evils and kick the secondary CPUs into INIT
> unless the system has installed special wakeup mechanisms which are not
> using INIT.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

For the whole series.

Reviewed-by: Ashok Raj <ashok.raj@...el.com>