KVM: retpolines: x86: eliminate retpoline from vmx.c exit handlers (4289d272) · Commits · 戴 / test

It's enough to check the exit value and issue a direct call to avoid the retpoline for all the common vmexit reasons. Of course CONFIG_RETPOLINE already forbids gcc to use indirect jumps while compiling all switch() statements, however switch() would still allow the compiler to bisect the case value. It's more efficient to prioritize the most frequent vmexits instead. The halt may be slow paths from the point of the guest, but not necessarily so from the point of the host if the host runs at full CPU capacity and no host CPU is ever left idle. Signed-off-by:

Andrea Arcangeli <aarcange@redhat.com> Signed-off-by:

Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/vmx.c

+16 −2

Original line number	Diff line number	Diff line
		@@ -5879,9 +5879,23 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
		}

		if (exit_reason < kvm_vmx_max_exit_handlers
		&& kvm_vmx_exit_handlers[exit_reason])
		&& kvm_vmx_exit_handlers[exit_reason]) {
		#ifdef CONFIG_RETPOLINE
		if (exit_reason == EXIT_REASON_MSR_WRITE)
		return kvm_emulate_wrmsr(vcpu);
		else if (exit_reason == EXIT_REASON_PREEMPTION_TIMER)
		return handle_preemption_timer(vcpu);
		else if (exit_reason == EXIT_REASON_PENDING_INTERRUPT)
		return handle_interrupt_window(vcpu);
		else if (exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
		return handle_external_interrupt(vcpu);
		else if (exit_reason == EXIT_REASON_HLT)
		return kvm_emulate_halt(vcpu);
		else if (exit_reason == EXIT_REASON_EPT_MISCONFIG)
		return handle_ept_misconfig(vcpu);
		#endif
		return kvm_vmx_exit_handlers[exit_reason](vcpu);
		else {
		} else {
		vcpu_unimpl(vcpu, "vmx: unexpected exit reason 0x%x\n",
		exit_reason);
		dump_vmcs();

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