linux-kernel - [PATCH v4 0/8] KVM: nVMX: Enlightened MSR Bitmap feature for Hyper-V on KVM (+ KVM: x86: MSR filtering and related fixes)

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Date:   Tue,  9 Nov 2021 17:28:27 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4 0/8] KVM: nVMX: Enlightened MSR Bitmap feature for Hyper-V on KVM (+ KVM: x86: MSR filtering and related fixes)

This series combines "Enlightened MSR Bitmap feature for Hyper-V on KVM v4"
and Sean's "KVM: x86: MSR filtering and related fixes v4" 
(https://lore.kernel.org/kvm/20211109013047.2041518-1-seanjc@google.com/)
series as they're code dependent.

Changes in "Enlightened MSR Bitmap feature for Hyper-V on KVM v4" since
 v3 [Sean]:
- Move Hyper-V Enlightened MSR Bitmap in vmx_create_vcpu() and expand
  the comment.
- Add R-b tag to "KVM: VMX: Introduce vmx_msr_bitmap_l01_changed() helper".
- s,msr_bitmap_force_recalc,force_msr_bitmap_recalc,
- Drop unneeded 'out_clear_msr_bitmap_force_recalc' path from "KVM: nVMX:
  Implement Enlightened MSR Bitmap feature".

Original description of the feature:

Updating MSR bitmap for L2 is not cheap and rearly needed. TLFS for Hyper-V
offers 'Enlightened MSR Bitmap' feature which allows L1 hypervisor to
inform L0 when it changes MSR bitmap, this eliminates the need to examine
L1's MSR bitmap for L2 every time when 'real' MSR bitmap for L2 gets
constructed.

When the feature is enabled for Win10+WSL2, it shaves off around 700 CPU
cycles from a nested vmexit cost (tight cpuid loop test).

First patch of the series is unrelated to the newly implemented feature,
it fixes a bug in Enlightened MSR Bitmap usage when KVM runs as a nested
hypervisor on top of Hyper-V.

Sean Christopherson (4):
  KVM: nVMX: Query current VMCS when determining if MSR bitmaps are in
    use
  KVM: nVMX: Handle dynamic MSR intercept toggling
  KVM: VMX: Macrofy the MSR bitmap getters and setters
  KVM: nVMX: Clean up x2APIC MSR handling for L2

Vitaly Kuznetsov (4):
  KVM: nVMX: Don't use Enlightened MSR Bitmap for L3
  KVM: VMX: Introduce vmx_msr_bitmap_l01_changed() helper
  KVM: nVMX: Track whether changes in L0 require MSR bitmap for L2 to be
    rebuilt
  KVM: nVMX: Implement Enlightened MSR Bitmap feature

 arch/x86/kvm/hyperv.c     |   2 +
 arch/x86/kvm/vmx/nested.c | 177 +++++++++++++++++---------------------
 arch/x86/kvm/vmx/vmx.c    |  94 +++++++-------------
 arch/x86/kvm/vmx/vmx.h    |  37 ++++++++
 4 files changed, 149 insertions(+), 161 deletions(-)

-- 
2.31.1