[Qemu-devel] Nested SVM only enabled (by default) in pc-i440fx-2.1?

[Qemu-devel] Nested SVM only enabled (by default) in pc-i440fx-2.1?

[Mark Kanda]

Hi all,

I noticed nested SVM is enabled only in pc-i440fx-2.1 (default is 
disabled); this was added when 2.1 was the latest:

	75d373ef97 ("target-i386: Disable SVM by default in KVM mode")

However, this change was not carried forward to newer machine types. Is 
this an oversight? Is there a reason we (still) need SVM disabled by 
default?

Default setting - target/i386/cpu.c:

	static PropValue kvm_default_props[] = {
	    { "kvmclock", "on" },
             ...
	    { "monitor", "off" },
	    { "svm", "off" },
	    { NULL, NULL },
	};

2.1 override - hw/i386/pc_piix.c:

	static void pc_compat_2_1_fn(MachineState *machine)
	{
	    pc_compat_2_2_fn(machine);
	    x86_cpu_change_kvm_default("svm", NULL);
	}

Thanks and best regards,
-Mark

Re: [Qemu-devel] Nested SVM only enabled (by default) in pc-i440fx-2.1?

[Mark Kanda]

On 2/27/2019 4:05 PM, Mark Kanda wrote:
> Hi all,
> 
> I noticed nested SVM is enabled only in pc-i440fx-2.1 (default is 
> disabled); this was added when 2.1 was the latest:
> 
>      75d373ef97 ("target-i386: Disable SVM by default in KVM mode")
> 
> However, this change was not carried forward to newer machine types. Is 
> this an oversight? Is there a reason we (still) need SVM disabled by 
> default?

To clarify, it's my understanding the above patch was added to disable 
nested SVM in pc-i440fx-2.2 (and future) machine types due to stability 
issues (while keeping it enabled in pc-i440fx-2.1 and previous machine 
types).

I'm wondering if nested SVM is now mature enough to remove this 
restriction and enable it by default (at least on recent machine types).

Thanks/regards,
-Mark