void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
{
	unsigned long old_cr4 = vcpu->arch.cr4;
	struct vcpu_vmx *vmx = to_vmx(vcpu);
	/*
	 * Pass through host's Machine Check Enable value to hw_cr4, which
	 * is in force while we are in guest mode.  Do not let guests control
	 * this bit, even if host CR4.MCE == 0.
	 */
	unsigned long hw_cr4;

	hw_cr4 = (cr4_read_shadow() & X86_CR4_MCE) | (cr4 & ~X86_CR4_MCE);
	if (is_unrestricted_guest(vcpu))
		hw_cr4 |= KVM_VM_CR4_ALWAYS_ON_UNRESTRICTED_GUEST;
	else if (vmx->rmode.vm86_active)
		hw_cr4 |= KVM_RMODE_VM_CR4_ALWAYS_ON;
	else
		hw_cr4 |= KVM_PMODE_VM_CR4_ALWAYS_ON;

	if (!boot_cpu_has(X86_FEATURE_UMIP) && vmx_umip_emulated()) {
		if (cr4 & X86_CR4_UMIP) {
			secondary_exec_controls_setbit(vmx, SECONDARY_EXEC_DESC);
			hw_cr4 &= ~X86_CR4_UMIP;
		} else if (!is_guest_mode(vcpu) ||
			!nested_cpu_has2(get_vmcs12(vcpu), SECONDARY_EXEC_DESC)) {
			secondary_exec_controls_clearbit(vmx, SECONDARY_EXEC_DESC);
		}
	}

	vcpu->arch.cr4 = cr4;
	kvm_register_mark_available(vcpu, VCPU_EXREG_CR4);

	if (!is_unrestricted_guest(vcpu)) {
		if (enable_ept) {
			if (!is_paging(vcpu)) {
				hw_cr4 &= ~X86_CR4_PAE;
				hw_cr4 |= X86_CR4_PSE;
			} else if (!(cr4 & X86_CR4_PAE)) {
				hw_cr4 &= ~X86_CR4_PAE;
			}
		}

		/*
		 * SMEP/SMAP/PKU is disabled if CPU is in non-paging mode in
		 * hardware.  To emulate this behavior, SMEP/SMAP/PKU needs
		 * to be manually disabled when guest switches to non-paging
		 * mode.
		 *
		 * If !enable_unrestricted_guest, the CPU is always running
		 * with CR0.PG=1 and CR4 needs to be modified.
		 * If enable_unrestricted_guest, the CPU automatically
		 * disables SMEP/SMAP/PKU when the guest sets CR0.PG=0.
		 */
		if (!is_paging(vcpu))
			hw_cr4 &= ~(X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_PKE);
	}

	vmcs_writel(CR4_READ_SHADOW, cr4);
	vmcs_writel(GUEST_CR4, hw_cr4);

	if ((cr4 ^ old_cr4) & (X86_CR4_OSXSAVE | X86_CR4_PKE))
		kvm_update_cpuid_runtime(vcpu);
}
Unknown