Re: [PATCH v3 1/2] hw/arm/imx8mp-evk: Add KVM support

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Nov 18, 2025 at 01:25:23PM +0100, BALATON Zoltan wrote:
> On Tue, 18 Nov 2025, Philippe Mathieu-Daudé wrote:
> > On 18/11/25 10:49, Bernhard Beschow wrote:
> > > Am 17. November 2025 17:38:03 UTC schrieb Peter Maydell
> > > <peter.maydell@linaro.org>:
> > > > On Mon, 17 Nov 2025 at 17:13, Cornelia Huck <cohuck@redhat.com> wrote:
> > > > > Running current master (resp. with this patch applied), I'm getting make
> > > > > check failures on an aarch64 (Mt. Snow) host ("qemu-system-aarch64:
> > > > > unknown type 'arm-gicv3'" while using this machine); going back right
> > > > > before this patch, everything works fine. Haven't tried to debug this
> > > > > yet (maybe I'm the one with the weird config again...)
> > > > 
> > > > Is this a KVM-only config (no TCG) ?
> > > > 
> > > > I think this happens because the KConfig now says
> > > > +    depends on TCG || KVM
> > > > 
> > > > but because the machine by default doesn't use KVM then
> > > > trying to run the machine with no extra arguments falls
> > > > over if TCG isn't present.
> > > > 
> > > > This thing we put in to handle "creation of the SoC object
> > > > via device introspection means it doesn't have an ms->cpu_type
> > > > to look at":
> > > > 
> > > > +    const char *cpu_type = ms->cpu_type ?:
> > > > ARM_CPU_TYPE_NAME("cortex-a53");
> > > > 
> > > > also probably won't do anything useful under a KVM-only config.
> > > > 
> > > > I think the simplest thing here is to put the KConfig back to:
> > > > 
> > > >   depends on TCG && AARCH64
> > > > 
> > > > People building a KVM-only config almost certainly do not
> > > > want this machine type and its devices, because the main
> > > > reason to build KVM-only is because you're in the
> > > > "virtualization use case" and want to not build in a
> > > > load of not-security-supported machine types.
> > > 
> > > Do we need this treatment for further machines, e.g. isapc, e500,
> > > mips? Or shall the CPU type handling in the SoC consider
> > > kvm_enabled()?
> > 
> > Good point. My understanding is only virt x86/arm/ppc64/s390x are
> > "security covered", but there is no explicit mention of that in
> > our doc. (btw why not include isapc? as it is a subset of other
> > covered x86 machines?)
> 
> Maybe because you can't run isapc with KVM because it's limited to Pentium
> but 32bit host support is removed? Or should we keep the ability to run it
> with newer CPUs for KVM?

32-bit host support removal is irrelevant. We still fully support 32-bit
guests, and they can use KVM. It is upto the user to disable the LM CPU
flag if they wish to, though it shouldn't matter because if the OS running
on isapc is that old it'll not even look for the "LM" flag to begin with,
and so the CPU will never get switchd into 64-bit mode. 

Note, a run of ./configure' with TCG disabled only is NOT claiming to be
providing a minimal virtualization build. It is simply discarding TCG.

If people want a minimal build, they're expected to customize the
KConfig files to suit their needs.

With regards,
Daniel
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