linux-kernel - Re: [PATCH v2 0/3] VMX: more nested fixes

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Date:   Thu, 21 Jan 2021 16:00:30 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Wanpeng Li <wanpengli@...cent.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org, Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v2 0/3] VMX: more nested fixes

On 14/01/21 21:54, Maxim Levitsky wrote:
> This is hopefully the last fix for VMX nested migration
> that finally allows my stress test of migration with a nested guest to pass.
> 
> In a nutshell after an optimization that was done in commit 7952d769c29ca,
> some of vmcs02 fields which can be modified by the L2 freely while it runs
> (like GSBASE and such) were not copied back to vmcs12 unless:
> 
> 1. L1 tries to vmread them (update done on intercept)
> 2. vmclear or vmldptr on other vmcs are done.
> 3. nested state is read and nested guest is running.
> 
> What wasn't done was to sync these 'rare' fields when L1 is running
> but still has a loaded vmcs12 which might have some stale fields,
> if that vmcs was used to enter a guest already due to that optimization.
> 
> Plus I added two minor patches to improve VMX tracepoints
> a bit. There is still a large room for improvement.
> 
> Best regards,
> 	Maxim Levitsky
> 
> Maxim Levitsky (3):
>    KVM: nVMX: Always call sync_vmcs02_to_vmcs12_rare on migration
>    KVM: nVMX: add kvm_nested_vmlaunch_resume tracepoint
>    KVM: VMX: read idt_vectoring_info a bit earlier
> 
>   arch/x86/kvm/trace.h      | 30 ++++++++++++++++++++++++++++++
>   arch/x86/kvm/vmx/nested.c | 19 ++++++++++++++-----
>   arch/x86/kvm/vmx/vmx.c    |  3 ++-
>   arch/x86/kvm/x86.c        |  1 +
>   4 files changed, 47 insertions(+), 6 deletions(-)
> 

I committed patch 1 since I need to send it out to Linus quite soonish, 
but please adjust and resend the others based on Sean's review.

Paolo