linux-kernel - Re: [PATCH v2 08/15] KVM: x86: Add Arch LBR MSRs to msrs_to_save

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Date:   Mon, 30 Jan 2023 20:27:49 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>
CC:     <pbonzini@...hat.com>, <jmattson@...gle.com>,
        <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <like.xu.linux@...il.com>, <kan.liang@...ux.intel.com>,
        <wei.w.wang@...el.com>
Subject: Re: [PATCH v2 08/15] KVM: x86: Add Arch LBR MSRs to msrs_to_save_all
 list


On 1/28/2023 5:43 AM, Sean Christopherson wrote:
> On Thu, Nov 24, 2022, Yang Weijiang wrote:
>> Arch LBR MSR_ARCH_LBR_DEPTH and MSR_ARCH_LBR_CTL are queried by
>> userspace application before it wants to {save|restore} the Arch LBR
>> data. Other LBR related data MSRs are omitted here intentionally due
>> to lengthy list(32*3). Userspace can still use KVM_{GET|SET}_MSRS to
>> access them if necessary.
> Absolutely not.  "there are a lot of them" isn't sufficient justification.  If
> the MSRs need to be migrated, then KVM needs to report them.  If the expectation
> is that XSAVES will handle them, then KVM needs to take a dependency on XSAVES
> when enabling arch LBRs.

OK, will add the full MSR list.