linux-kernel - Re: [PATCH v2 0/3] x86/crash: Fix double NMI shootdown bug

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Message-ID: <Ysi9pVFHsqM3uivr@google.com>
Date:   Fri, 8 Jul 2022 23:28:37 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v2 0/3] x86/crash: Fix double NMI shootdown bug

On Wed, May 18, 2022, Sean Christopherson wrote:
> Fix a double NMI shootdown bug found and debugged by Guilherme, who did all
> the hard work.  NMI shootdown is a one-time thing; the handler leaves NMIs
> blocked and enters halt.  At best, a second (or third...) shootdown is an
> expensive nop, at worst it can hang the kernel and prevent kexec'ing into
> a new kernel, e.g. prior to the hardening of register_nmi_handler(), a
> double shootdown resulted in a double list_add(), which is fatal when running
> with CONFIG_BUG_ON_DATA_CORRUPTION=y.

...

> Sean Christopherson (3):
>   x86/crash: Disable virt in core NMI crash handler to avoid double
>     shootdown
>   x86/reboot: Disable virtualization in an emergency if SVM is supported
>   x86/virt: Fold __cpu_emergency_vmxoff() into its sole caller
> 
>  arch/x86/include/asm/reboot.h  |  1 +
>  arch/x86/include/asm/virtext.h | 14 +-----
>  arch/x86/kernel/crash.c        | 16 +-----
>  arch/x86/kernel/reboot.c       | 89 +++++++++++++++++++++++++---------
>  4 files changed, 69 insertions(+), 51 deletions(-)

Ping!  Still applies cleanly.