Re: [PATCH 1/2] KVM: x86: Invert APICv/AVIC enablement check

From: Sean Christopherson
Date: Mon May 17 2021 - 17:26:43 EST


On Mon, May 17, 2021, Jim Mattson wrote:
> On Mon, May 17, 2021 at 2:03 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> >
> > On Thu, May 13, 2021, Vitaly Kuznetsov wrote:
> > > Currently, APICv/AVIC enablement is global ('enable_apicv' module parameter
> > > for Intel, 'avic' module parameter for AMD) but there's no way to check
> > > it from vendor-neutral code. Add 'apicv_supported()' to kvm_x86_ops and
> > > invert kvm_apicv_init() (which now doesn't need to be called from arch-
> > > specific code).
> >
> > Rather than add a new hook, just move the variable to x86.c, and export it so
> > that VMX and SVM can give it different module names. The only hiccup is that
> > avic is off by default, but I don't see why that can't be changed.
>
> See https://www.spinics.net/lists/kvm/msg208722.html.

Boo. A common enable_apicv can still work, SVM just needs an intermediary
between the module param and enable_apicv.

--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -185,6 +185,10 @@ module_param(vls, int, 0444);
static int vgif = true;
module_param(vgif, int, 0444);

+/* enable / disable AVIC */
+static bool avic;
+module_param(avic, bool, S_IRUGO);
+
bool __read_mostly dump_invalid_vmcb;
module_param(dump_invalid_vmcb, bool, 0644);

@@ -1009,16 +1013,19 @@ static __init int svm_hardware_setup(void)
nrips = false;
}

- if (avic) {
- if (!npt_enabled ||
- !boot_cpu_has(X86_FEATURE_AVIC) ||
- !IS_ENABLED(CONFIG_X86_LOCAL_APIC)) {
- avic = false;
- } else {
- pr_info("AVIC enabled\n");
+ if (!npt_enabled || !boot_cpu_has(X86_FEATURE_AVIC))
+ avic = false;

- amd_iommu_register_ga_log_notifier(&avic_ga_log_notifier);
- }
+ /*
+ * Override the common enable_apicv. AVIC is disabled by default
+ * because Jim said so.
+ */
+ enable_apicv = avic;
+
+ if (enable_apicv) {
+ pr_info("AVIC enabled\n");
+
+ amd_iommu_register_ga_log_notifier(&avic_ga_log_notifier);
}

if (vls) {