linux-kernel - Re: [PATCH] KVM: nVMX: Fix CR4 after VMLAUNCH/VMRESUME failure

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Date:   Thu, 8 Feb 2018 14:22:13 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH] KVM: nVMX: Fix CR4 after VMLAUNCH/VMRESUME failure

2018-02-08 0:57 GMT+08:00 Jim Mattson <jmattson@...gle.com>:
> vmcs12->host_cr[34] does not contain the up-to-date values when L1 is
> running. L1 can vmwrite any values there. We know at this point that

It will incur a vmexit to emulate L1 vmwrites vmcs12->host_cr[34] even
if vmcs shadow is enabled since host_cr[34] is not shadowed in the
bitmap, why it is not up-to-date when L1 is running?

Regards,
Wanpeng Li

> they are legal (because we checked them), but that's about it. If the
> VMLAUNCH/VMRESUME of vmcs12 fails for "invalid control field," there
> is no VM-exit from L2 to L1, and these fields are not loaded. Instead,
> execution just falls through to the next instruction with VMFailValid
> semantics.
>
> On Wed, Feb 7, 2018 at 12:31 AM, Wanpeng Li <kernellwp@...il.com> wrote:
>> 2018-02-07 0:58 GMT+08:00 Jim Mattson <jmattson@...gle.com>:
>>> On Mon, Feb 5, 2018 at 4:57 PM, Wanpeng Li <kernellwp@...il.com> wrote:
>>>
>>>> This is effective one, what I restore in this patch is
>>>> achitectural/guest visible.
>>>
>>> This patch doesn't "restore" the guest visible CR4 to its value at the
>>> time of VMLAUNCH/VMRESUME. It loads a new CR4 value from the vmcs12.
>>> That behavior is incorrect.
>>
>> You have another pointing out about this.
>> https://lkml.org/lkml/2018/2/5/518 vmcs12->host_cr3/host_cr4 has the
>> up-to-date value when L1 is running, it is still up-to-date after
>> vmexit due to L1 executes VMLAUNCH/VMRESUME, I think the value stays
>> the same before L0 emulates the VMLAUNCH/VMRESUME, according to below
>> comments, why vmcs12->host_cr3/cr4 is not the value which we should
>> restore?
>>
>> * After an early L2 VM-entry failure, we're now back
>> * in L1 which thinks it just finished a VMLAUNCH or
>> * VMRESUME instruction
>>
>> Regards,
>> Wanpeng Li