Re: [PATCH v2] docs/virt/kvm: Document running nested guests

[Kashyap Chamarthy <kchamart@redhat.com>]

On Tue, Apr 21, 2020 at 12:35:21PM +0200, Paolo Bonzini wrote:
> Mostly looks good except for kernel parameters:

[Just noticed this; somehow the KVM e-mails, which I explicitly Cced
myself, aren't arriving in my Inbox.]

> On 20/04/20 13:17, Kashyap Chamarthy wrote:
> > +Enabling "nested" (x86)
> > +-----------------------
> > +
> > +From Linux kernel v4.19 onwards, the ``nested`` KVM parameter is enabled
> > +by default for Intel x86, but *not* for AMD.  (Though your Linux
> > +distribution might override this default.)
> 
> It is enabled for AMD as well.

Ah, thanks.  Will correct.

> > +
> > +If your hardware is sufficiently advanced (Intel Haswell processor or
> > +above which has newer hardware virt extensions), you might want to
> > +enable additional features: "Shadow VMCS (Virtual Machine Control
> > +Structure)", APIC Virtualization on your bare metal host (L0).
> > +Parameters for Intel hosts::
> > +
> > +    $ cat /sys/module/kvm_intel/parameters/enable_shadow_vmcs
> > +    Y
> > +
> > +    $ cat /sys/module/kvm_intel/parameters/enable_apicv
> > +    N
> > +
> > +    $ cat /sys/module/kvm_intel/parameters/ept
> > +    Y
> 
> 
> These are enabled by default if you have them, on all kernel versions.
> So you may instead tell people to check them (especially
> enable_shadow_vmcs and ept) if their L2 guests run slower.

Noted, will amend.

> > 
> > +Starting a nested guest (x86)
> > +-----------------------------
> > +
> > +Once your bare metal host (L0) is configured for nesting, you should be
> > +able to start an L1 guest with::
> > +
> > +    $ qemu-kvm -cpu host [...]
> > +
> > +The above will pass through the host CPU's capabilities as-is to the
> > +gues); or for better live migration compatibility, use a named CPU
> > +model supported by QEMU. e.g.::
> > +
> > +    $ qemu-kvm -cpu Haswell-noTSX-IBRS,vmx=on
> > +
> > +then the guest hypervisor will subsequently be capable of running a
> > +nested guest with accelerated KVM.
> > +
> 
> The latter is only on QEMU 4.2 and newer.  Also, you should group by
> architecture and use third-level headings within an architecture.

Okay, will adjust the structure.

Thanks for the review.


-- 
/kashyap