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From: Yu Zhang <yu.c.zhang@linux.intel.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Hou Wenlong <houwenlong93@linux.alibaba.com>,
	kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Jan Kiszka <jan.kiszka@siemens.com>, Avi Kivity <avi@redhat.com>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 1/3] kvm: x86: Introduce hypercall x86 ops for handling hypercall not in cpl0
Date: Fri, 10 Sep 2021 09:53:51 +0800	[thread overview]
Message-ID: <20210910015351.yxvgv2nedgojmmeo@linux.intel.com> (raw)
In-Reply-To: <YTo/t4G1iI28oDmk@google.com>

On Thu, Sep 09, 2021 at 05:09:11PM +0000, Sean Christopherson wrote:
> On Fri, Sep 10, 2021, Yu Zhang wrote:
> > 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).
> 
> Correct, VMCALL unconditionally causes VM-Exit in non-root mode, but Hou is
> referring to the first fault condition of "non VMX operation".  The intent of the
> patch is to emulate hardware behavior for CPL>0: if L1 is not in VMX operation,
> a.k.a. not post-VMXON, then #UD, else #GP (because VMCALL #GPs at CPL>0 in VMX
> root).

Oh, I see. It's to make the virtualized world more real. But like you said, 
it's not KVM's target. And doing that could cause more problems - a PV guest
expects the VMCALL to succeed, regardless it has VMX capability or its VMX is
on or not.

Thanks for the explaination.

B.R.
Yu

  reply	other threads:[~2021-09-10  1:54 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-09 11:37 [PATCH 0/3] some fixes of hypercall emulation Hou Wenlong
2021-09-09 11:37 ` [PATCH 1/3] kvm: x86: Introduce hypercall x86 ops for handling hypercall not in cpl0 Hou Wenlong
2021-09-09 11:37 ` [PATCH 2/3] kvm: x86: Refactor kvm_emulate_hypercall() to no skip instruction Hou Wenlong
2021-09-09 11:37 ` [PATCH 3/3] kvm: x86: Emulate hypercall instead of fixing hypercall instruction Hou Wenlong
2021-09-09 11:55 ` [PATCH v2 0/3] kvm: x86: some fixes of hypercall emulation Hou Wenlong
2021-09-09 11:55   ` [PATCH v2 1/3] kvm: x86: Introduce hypercall x86 ops for handling hypercall not in cpl0 Hou Wenlong
2021-09-09 16:39     ` Yu Zhang
2021-09-09 17:09       ` Sean Christopherson
2021-09-10  1:53         ` Yu Zhang [this message]
2021-09-09 11:55   ` [PATCH v2 2/3] kvm: x86: Refactor kvm_emulate_hypercall() to no skip instruction Hou Wenlong
2021-09-09 11:55   ` [PATCH v2 3/3] kvm: x86: Emulate hypercall instead of fixing hypercall instruction Hou Wenlong
2021-09-16 16:00     ` Sean Christopherson

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