linux-kernel - Re: [PATCH v11 14/16] KVM: x86/vmx: Flip Arch LBREn bit on guest state change

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Date:   Tue, 17 May 2022 11:01:05 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Yang, Weijiang" <weijiang.yang@...el.com>
Cc:     "jmattson@...gle.com" <jmattson@...gle.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "kan.liang@...ux.intel.com" <kan.liang@...ux.intel.com>,
        "like.xu.linux@...il.com" <like.xu.linux@...il.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "Wang, Wei W" <wei.w.wang@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v11 14/16] KVM: x86/vmx: Flip Arch LBREn bit on guest
 state change

On 5/17/22 10:56, Yang, Weijiang wrote:
>> I added more things to ease migration handling in SMM because: 1) qemu 
>> checks LBREn before transfer Arch LBR MSRs.

I think it should always transfer them instead?  There's time to post a 
fixup patch.

>> 2) Perf event is created when 
>> LBREn is being set.  Two things are not certain: 1) IA32_LBR_CTL doesn't have 
>> corresponding slot in SMRAM,not sure if we need to rely on it to transfer the MSR.
>> I chose 0x7f10 as the offset(CET takes 0x7f08) for storage, need you double check if 
>> it's free or used.

0x7f10 sounds good.

> Hi, Paolo,
> 
> I found there're some rebase conflicts between this series and your kvm 
> queue branch due to PEBS patches, I can re-post a new version based on
> your queue branch if necessary.

Yes, please.

> Waiting for your comments on this patch...

I already commented that using bit 63 is not good, didn't I?

Paolo