Re: [PATCH v5 0/5] ARM Nested Virt Support

[Marc Zyngier <maz@kernel.org>]

On Tue, 27 May 2025 14:11:41 +0100,
Eric Auger <eric.auger@redhat.com> wrote:
> 
> Hi Miguel, Marc,
> 
> On 5/27/25 2:54 PM, Miguel Luis wrote:
> >
> >> On 27 May 2025, at 12:01, Marc Zyngier <maz@kernel.org> wrote:
> >>
> >> On Tue, 27 May 2025 12:33:23 +0100,
> >> Miguel Luis <miguel.luis@oracle.com> wrote:
> >>> Hi Eric,
> >>>
> >>>> On 27 May 2025, at 06:24, Eric Auger <eric.auger@redhat.com> wrote:
> >>>>
> >>>> Now that ARM nested virt has landed in kvm/next, let's turn the series
> >>>> into a PATCH series. The linux header update was made against kvm/next.
> >>>>
> >>>> For gaining virt functionality in KVM accelerated L1, The host needs to
> >>>> be booted with "kvm-arm.mode=nested" option and qemu needs to be invoked
> >>>> with: -machine virt,virtualization=on.
> >>> For the current kvmarm/next the guest also needs
> >>> “kvm-arm.mode=nested” I believe.
> >> No, unless you want the guest itself to be NV-capable.
> Effectively you don't need "kvm-arm.mode=nested" except if you want want
> multiple level of nesting.

You need kvm-arm.mode=nested on the command-line of a kernel that acts
as a host exposing KVM_CAP_ARM_EL2. This is obviously a recursive
property, but that's for the user to decide if they want it or not.

> > Correct, I got carried away with some mode combinations. Maybe we should depict
> > here more broadly how NV might be used with different mode combinations. I'll
> > think about this further ahead.
> >
> > As far this series go I couldn't found any issue booting a L1 guest with
> > virtualization=on and a L2 guest with virtualization=off.
> 
> on my end I tested with various untouched L2 guests (debian, fed, rhel)
> in 4kB/4kB/4KB page size mode (host, L1, L2). Those configs were successful.

I'm doing 4/4/4 (x1e) and 16/16/4 (m2). I'm also doing 4/4/4/4/4, but
that's not very reliable yet,

> with 64kB/64kB/64kB configs I am less lucky atm. One one machine I
> cannot boot L1 with virtualization=on. On the other I can boot L1 but
> cannot boot L2.

I think x1e supports 64k pages, but I'd need to try. Not exactly the
highest priority on my list of things to debug.

> Trying my best to debug a little bit further with my setup. Anyway if
> somebody else can try 64kB configs, it would help to confirm whether
> there are pending issues. I don't think they are related to this qemu
> integration series though.

Yeah, definitely a kernel issue IMO.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.