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Sean Christopherson authored
Unconditionally check the validity of the incoming CR3 during nested VM-Enter/VM-Exit to avoid invoking kvm_read_cr3() in the common case where the guest isn't using PAE paging. If vmcs.GUEST_CR3 hasn't yet been cached (common case), kvm_read_cr3() will trigger a VMREAD. The VMREAD (~30 cycles) alone is likely slower than nested_cr3_valid() (~5 cycles if vcpu->arch.maxphyaddr gets a cache hit), and the poor exchange only gets worse when retpolines are enabled as the call to kvm_x86_ops.cache_reg() will incur a retpoline (60+ cycles). Signed-off-by:
Sean Christopherson <sean.j.christopherson@intel.com> Message-Id: <20200502043234.12481-3-sean.j.christopherson@intel.com> Signed-off-by:
Paolo Bonzini <pbonzini@redhat.com>
0cc69204