linux-kernel - Re: [PATCH v4 07/19] x86/reboot: Disable virtualization during reboot iff callback is registered

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Message-ID: <7fcc0a4b3b653bfc9c031a3ca060e4cd14119228.camel@intel.com>
Date:   Mon, 24 Jul 2023 23:57:46 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Gao, Chao" <chao.gao@...el.com>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>
Subject: Re: [PATCH v4 07/19] x86/reboot: Disable virtualization during reboot
 iff callback is registered

On Fri, 2023-07-21 at 13:18 -0700, Sean Christopherson wrote:
> Attempt to disable virtualization during an emergency reboot if and only
> if there is a registered virt callback, i.e. iff a hypervisor (KVM) is
> active.  If there's no active hypervisor, then the CPU can't be operating
> with VMX or SVM enabled (barring an egregious bug).
> 
> Checking for a valid callback instead of simply for SVM or VMX support
> can also eliminates spurious NMIs by avoiding the unecessary call to
> nmi_shootdown_cpus_on_restart().
> 
> Note, IRQs are disabled, which prevents KVM from coming along and
> enabling virtualization after the fact.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> 

Reviewed-by: Kai Huang <kai.huang@...el.com>