linux-kernel - Re: [PATCH v3 06/18] x86/reboot: Assert that IRQs are disabled when turning off virtualization

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Message-ID: <a135f18eeab880f002c7748da3aff8ed0c8c63e3.camel@intel.com>
Date:   Mon, 22 May 2023 13:05:50 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.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 v3 06/18] x86/reboot: Assert that IRQs are disabled when
 turning off virtualization

On Fri, 2023-05-12 at 16:50 -0700, Sean Christopherson wrote:
> Assert that IRQs are disabled when turning off virtualization in an
> emergency.  KVM enables hardware via on_each_cpu(), i.e. could re-enable
> hardware if a pending IPI were delivered after disabling virtualization.
> 
> Remove a misleading comment from emergency_reboot_disable_virtualization()
> about "just" needing to guarantee the CPU is stable (see above).
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

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

> ---
>  arch/x86/kernel/reboot.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
> index 20f7bdabc52e..fddfea5f1d20 100644
> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -531,7 +531,6 @@ static inline void nmi_shootdown_cpus_on_restart(void);
>  
>  static void emergency_reboot_disable_virtualization(void)
>  {
> -	/* Just make sure we won't change CPUs while doing this */
>  	local_irq_disable();
>  
>  	/*
> @@ -820,6 +819,13 @@ void cpu_emergency_disable_virtualization(void)
>  {
>  	cpu_emergency_virt_cb *callback;
>  
> +	/*
> +	 * IRQs must be disabled as KVM enables virtualization in hardware via
> +	 * function call IPIs, i.e. IRQs need to be disabled to guarantee
> +	 * virtualization stays disabled.
> +	 */
> +	lockdep_assert_irqs_disabled();
> +
>  	rcu_read_lock();
>  	callback = rcu_dereference(cpu_emergency_virt_callback);
>  	if (callback)
> -- 
> 2.40.1.606.ga4b1b128d6-goog
>