Re: [PATCH v3 33/33] KVM: PPC: Book3S HV: Add a VM capability to enable nested virtualization

On Thu, Oct 04, 2018 at 07:48:26PM +1000, Paul Mackerras wrote:

On Wed, Oct 03, 2018 at 04:21:44PM +1000, David Gibson wrote:

quoted

On Tue, Oct 02, 2018 at 09:31:32PM +1000, Paul Mackerras wrote:

quoted

With this, userspace can enable a KVM-HV guest to run nested guests
under it.

[snip]

quoted

quoted

+/* If set, guests are allowed to create and control nested guests */
+static bool enable_nested = true;
+module_param(enable_nested, bool, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(enable_nested, "Enable nested virtualization (only on POWER9)");

I'd suggest calling the module parameter just "nested" to match x86.

OK.

quoted

quoted

 /* If set, the threads on each CPU core have to be in the same MMU mode */
 static bool no_mixing_hpt_and_radix;
 

@@ -5188,6 +5193,17 @@ static int kvmhv_configure_mmu(struct kvm *kvm, struct kvm_ppc_mmuv3_cfg *cfg)
 	return err;
 }
 
+static int kvmhv_enable_nested(struct kvm *kvm, bool enable)
+{
+	if (!(enable_nested && cpu_has_feature(CPU_FTR_ARCH_300)))
+		return -EINVAL;

Maybe EPERM, rather than EINVAL.  There's nothing invalid about the
ioctl() parameters - we just can't do what they want.

Just for pedantry's sake, I'll make it EPERM for !enable_nested and
ENODEV for !POWER9. :)

Sounds fair.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson