linux-kernel - Re: [PATCH v2 1/3] kvm: x86: Introduce hypercall x86 ops for handling hypercall not in cpl0

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Date:   Fri, 10 Sep 2021 00:39:01 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Hou Wenlong <houwenlong93@...ux.alibaba.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Avi Kivity <avi@...hat.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] kvm: x86: Introduce hypercall x86 ops for
 handling hypercall not in cpl0

On Thu, Sep 09, 2021 at 07:55:23PM +0800, Hou Wenlong wrote:
> Per Intel's SDM, use vmcall instruction in non VMX operation for cpl3
> it should trigger a #UD. And in VMX root operation, it should

Are you sure? IIRC, vmcall will always cause VM exit as long as CPU
is in non-root mode(regardless the CPL).

Also, could you please explain why skipping the vmcall would cause
exception in the host? Thanks!

B.R.
Yu