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* [PATCH 0/4] KVM: nVMX: Use vmcs01 ctrls shadow as basis for vmcs02
@ 2021-08-10 17:19 Sean Christopherson
  2021-08-10 17:19 ` [PATCH 1/4] KVM: VMX: Use current VMCS to query WAITPKG support for MSR emulation Sean Christopherson
                   ` (4 more replies)
  0 siblings, 5 replies; 6+ messages in thread
From: Sean Christopherson @ 2021-08-10 17:19 UTC (permalink / raw)
  To: Paolo Bonzini
  Cc: Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
	Joerg Roedel, kvm, linux-kernel, Zeng Guang

The goal of this series is to drop the vmx->secondary_exec_control cache
without degrading nested VM-Enter performance.  The cache is effective,
e.g. saves ~1000 cycles on nested VM-Enter, but confusing.  The worst of
the confusion could be eliminated by returning the computed value from
vmx_compute_secondary_exec_control() to make the calls to the "compute"
helper more like the other controls.  But, the nested VM-Enter path would
still have special handling for secondary exec controls, and ideally all
controls would benefit from caching, though the benefits are marginal for
other controls and thus difficult to justify.

Happily, vmcs01 already caches the calculated controls in the
controls_shadow.  The only issue is that the controls_shadow may have
dynamically toggled bits set.  However, that is not a fundamental problem,
it's simply different than what is expected by the nested VM-Enter code
and is easily remedied.

TL;DR: Get KVM's (L0's) desires for vmcs02 controls from vmcs01's
controls_shadow instead of recalculating the desired controls on every
nested VM-Enter, thus eliminating the need to have a dedicated cache for
the secondary exec controls calulation.

Sean Christopherson (4):
  KVM: VMX: Use current VMCS to query WAITPKG support for MSR emulation
  KVM: nVMX: Pull KVM L0's desired controls directly from vmcs01
  KVM: VMX: Drop caching of KVM's desired sec exec controls for vmcs01
  KVM: VMX: Hide VMCS control calculators in vmx.c

 arch/x86/kvm/vmx/nested.c | 25 ++++++++++++--------
 arch/x86/kvm/vmx/vmx.c    | 48 +++++++++++++++++++++++++++------------
 arch/x86/kvm/vmx/vmx.h    | 35 +++++-----------------------
 3 files changed, 56 insertions(+), 52 deletions(-)

-- 
2.32.0.605.g8dce9f2422-goog


^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-08-10 17:43 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-08-10 17:19 [PATCH 0/4] KVM: nVMX: Use vmcs01 ctrls shadow as basis for vmcs02 Sean Christopherson
2021-08-10 17:19 ` [PATCH 1/4] KVM: VMX: Use current VMCS to query WAITPKG support for MSR emulation Sean Christopherson
2021-08-10 17:19 ` [PATCH 2/4] KVM: nVMX: Pull KVM L0's desired controls directly from vmcs01 Sean Christopherson
2021-08-10 17:19 ` [PATCH 3/4] KVM: VMX: Drop caching of KVM's desired sec exec controls for vmcs01 Sean Christopherson
2021-08-10 17:19 ` [PATCH 4/4] KVM: VMX: Hide VMCS control calculators in vmx.c Sean Christopherson
2021-08-10 17:39 ` [PATCH 0/4] KVM: nVMX: Use vmcs01 ctrls shadow as basis for vmcs02 Paolo Bonzini

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