linux-kernel - Re: [PATCH 2/4] KVM: VMX: Handle #MCs on VM-Enter/TD-Enter outside of the fastpath

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Message-ID: <aRsXVvDHsdCjEgPM@tlindgre-MOBL1>
Date: Mon, 17 Nov 2025 14:38:46 +0200
From: Tony Lindgren <tony.lindgren@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>,
	"Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jon Kohler <jon@...anix.com>
Subject: Re: [PATCH 2/4] KVM: VMX: Handle #MCs on VM-Enter/TD-Enter outside
 of the fastpath

Hi,

On Thu, Oct 30, 2025 at 03:42:44PM -0700, Sean Christopherson wrote:
> --- a/arch/x86/kvm/vmx/main.c
> +++ b/arch/x86/kvm/vmx/main.c
> @@ -608,6 +608,17 @@ static void vt_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa,
>  	vmx_load_mmu_pgd(vcpu, root_hpa, pgd_level);
>  }
>  
> +static void vt_handle_exit_irqoff(struct kvm_vcpu *vcpu)
> +{
> +	if (unlikely((u16)vmx_get_exit_reason(vcpu).basic == EXIT_REASON_MCE_DURING_VMENTRY))
> +		kvm_machine_check();
> +
> +	if (is_td_vcpu(vcpu))
> +		return;
> +
> +	return vmx_handle_exit_irqoff(vcpu);
> +}

I bisected kvm-x86/next down to this change for a TDX guest not booting
and host producing errors like:

watchdog: CPU118: Watchdog detected hard LOCKUP on cpu 118

Dropping the is_td_vcpu(vcpu) check above fixes the issue. Earlier the
call for vmx_handle_exit_irqoff() was unconditional.

Probably the (u16) cast above can be dropped too? It was never used for
TDX looking at the patch.

Regards,

Tony