linux-kernel - Re: [FYI PATCH 1/3] KVM: nVMX: Don't emulate instructions in guest mode

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Message-ID: <41d80479-7dbc-d912-ff0e-acd48746de0f@web.de>
Date:   Sat, 29 Feb 2020 19:00:43 +0100
From:   Jan Kiszka <jan.kiszka@....de>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     oupton@...gle.com, stable@...r.kernel.org
Subject: Re: [FYI PATCH 1/3] KVM: nVMX: Don't emulate instructions in guest
 mode

On 24.02.20 19:56, Paolo Bonzini wrote:
> vmx_check_intercept is not yet fully implemented. To avoid emulating
> instructions disallowed by the L1 hypervisor, refuse to emulate
> instructions by default.
>
> Cc: stable@...r.kernel.org
> [Made commit, added commit msg - Oliver]
> Signed-off-by: Oliver Upton <oupton@...gle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>   arch/x86/kvm/vmx/vmx.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index dcca514ffd42..5801a86f9c24 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7164,7 +7164,7 @@ static int vmx_check_intercept(struct kvm_vcpu *vcpu,
>   	}
>
>   	/* TODO: check more intercepts... */
> -	return X86EMUL_CONTINUE;
> +	return X86EMUL_UNHANDLEABLE;
>   }
>
>   #ifdef CONFIG_X86_64
>

Is this expected to cause regressions on less common workloads?
Jailhouse as L1 now fails when Linux as L2 tries to boot a CPU: L2-Linux
gets a triple fault on load_current_idt() in start_secondary(). Only
bisected so far, didn't debug further.

Jan