Re: [PATCH 2/2] KVM: nSVM: improve SYSENTER emulation on AMD

[Paolo Bonzini <pbonzini@redhat.com>]

On 15/03/21 18:43, Maxim Levitsky wrote:
> +	if (!guest_cpuid_is_intel(vcpu)) {
> +		/*
> +		 * If hardware supports Virtual VMLOAD VMSAVE then enable it
> +		 * in VMCB and clear intercepts to avoid #VMEXIT.
> +		 */
> +		if (vls) {
> +			svm_clr_intercept(svm, INTERCEPT_VMLOAD);
> +			svm_clr_intercept(svm, INTERCEPT_VMSAVE);
> +			svm->vmcb->control.virt_ext |= VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK;
> +		}
> +		/* No need to intercept these msrs either */
> +		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_EIP, 1, 1);
> +		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_ESP, 1, 1);
> +	}

An "else" is needed here to do the opposite setup (removing the "if 
(vls)" from init_vmcb).

This also makes the code more readable since you can write

	if (guest_cpuid_is_intel(vcpu)) {
		/*
		 * We must intercept SYSENTER_EIP and SYSENTER_ESP
		 * accesses because the processor only stores 32 bits.
		 * For the same reason we cannot use virtual
		 * VMLOAD/VMSAVE.
		 */
		...
	} else {
		/* Do the opposite.  */
		...
	}

Paolo