linux-kernel - Re: [PATCH] KVM: VMX: Flush shadow VMCS on emergency reboot

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Message-ID: <d8d043e6ddfc7c815809b25a1c76c11dbb67d873.camel@intel.com>
Date: Mon, 31 Mar 2025 23:17:24 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Gao, Chao"
	<chao.gao@...el.com>
CC: "seanjc@...gle.com" <seanjc@...gle.com>, "x86@...nel.org"
	<x86@...nel.org>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>, "hpa@...or.com" <hpa@...or.com>,
	"mingo@...hat.com" <mingo@...hat.com>, "tglx@...utronix.de"
	<tglx@...utronix.de>, "bp@...en8.de" <bp@...en8.de>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>
Subject: Re: [PATCH] KVM: VMX: Flush shadow VMCS on emergency reboot

On Mon, 2025-03-24 at 22:08 +0800, Chao Gao wrote:
> Ensure the shadow VMCS cache is evicted during an emergency reboot to
> prevent potential memory corruption if the cache is evicted after reboot.
> 
> This issue was identified through code inspection, as __loaded_vmcs_clear()
> flushes both the normal VMCS and the shadow VMCS.
> 
> Avoid checking the "launched" state during an emergency reboot, unlike the
> behavior in __loaded_vmcs_clear(). This is important because reboot NMIs
> can interfere with operations like copy_shadow_to_vmcs12(), where shadow
> VMCSes are loaded directly using VMPTRLD. In such cases, if NMIs occur
> right after the VMCS load, the shadow VMCSes will be active but the
> "launched" state may not be set.
> 
> Signed-off-by: Chao Gao <chao.gao@...el.com>

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

> ---
>  arch/x86/kvm/vmx/vmx.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index b70ed72c1783..dccd1c9939b8 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -769,8 +769,11 @@ void vmx_emergency_disable_virtualization_cpu(void)
>  		return;
>  
>  	list_for_each_entry(v, &per_cpu(loaded_vmcss_on_cpu, cpu),
> -			    loaded_vmcss_on_cpu_link)
> +			    loaded_vmcss_on_cpu_link) {
>  		vmcs_clear(v->vmcs);
> +		if (v->shadow_vmcs)
> +			vmcs_clear(v->shadow_vmcs);
> +	}
>  
>  	kvm_cpu_vmxoff();
>  }