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KVM: nVMX: Skip IBPB when switching between vmcs01 and vmcs02
Skip the Indirect Branch Prediction Barrier that is triggered on a VMCS switch when running with spectre_v2_user=on/auto if the switch is between two VMCSes in the same guest, i.e. between vmcs01 and vmcs02. The IBPB is intended to prevent one guest from attacking another, which is unnecessary in the nested case as it's the same guest from KVM's perspective. This all but eliminates the overhead observed for nested VMX transitions when running with CONFIG_RETPOLINE=y and spectre_v2_user=on/auto, which can be significant, e.g. roughly 3x on current systems. Reported-by: Alexander Graf <graf@amazon.com> Cc: KarimAllah Raslan <karahmed@amazon.de> Cc: stable@vger.kernel.org Fixes: 15d4507 ("KVM/x86: Add IBPB support") Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Message-Id: <20200501163117.4655-1-sean.j.christopherson@intel.com> [Invert direction of bool argument. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Sean Christopherson
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Paolo Bonzini
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May 13, 2020
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