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From:   Jim Mattson <jmattson@google.com>
Date:   Fri, 9 Jul 2021 15:54:53 -0700
Message-ID: <CALMp9eQEs9pUyy1PpwLPG0_PtF07tR2Opw+1b=w4-knOwYPvvg@mail.gmail.com>
Subject: Re: [PATCH v5 06/13] KVM: x86/vmx: Save/Restore host MSR_ARCH_LBR_CTL state
To:     Yang Weijiang <weijiang.yang@intel.com>
Cc:     pbonzini@redhat.com, seanjc@google.com, vkuznets@redhat.com,
        wei.w.wang@intel.com, like.xu.linux@gmail.com, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Fri, Jul 9, 2021 at 2:51 AM Yang Weijiang <weijiang.yang@intel.com> wrote:
>
> If host is using MSR_ARCH_LBR_CTL then save it before vm-entry
> and reload it after vm-exit.

I don't see anything being done here "before VM-entry" or "after
VM-exit." This code seems to be invoked on vcpu_load and vcpu_put.

In any case, I don't see why this one MSR is special. It seems that if
the host is using the architectural LBR MSRs, then *all* of the host
architectural LBR MSRs have to be saved on vcpu_load and restored on
vcpu_put. Shouldn't  kvm_load_guest_fpu() and kvm_put_guest_fpu() do
that via the calls to kvm_save_current_fpu(vcpu->arch.user_fpu) and
restore_fpregs_from_fpstate(&vcpu->arch.user_fpu->state)?