[PATCH 2/5] arm: qemu: enable LPAE on 32-bit

[Ard Biesheuvel]

On Sat, 6 Jun 2020 at 22:49, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>
> On 6/6/20 10:32 PM, Heinrich Schuchardt wrote:
> > On 6/6/20 7:15 PM, Ard Biesheuvel wrote:
> >> QEMU's mach-virt machine only supports selecting CPU models that
> >> implement the virtualization extensions, and are therefore guaranteed
> >> to support LPAE as well.
> >
> > I wonder why
> > qemu-system-arm -machine virt -cpu help
> > lists cortex-a9 (which is not LPAE enabled).
> >
> > But when I try to use it I get
> > qemu-system-arm: mach-virt: CPU type cortex-a9-arm-cpu not supported
> > This looks like a missing feature in QEMU.
> >

This is not a missing feature. The virt board uses PSCI for powerdown
and reset, and to bring up secondary cores.
PSCI requires the HVC instruction, which is only available if the virt
extensions are implemented.

So emulating CPUs without the virt extensions would require a
replacement for PSCI to be implemented as well, which seems rather
pointless to me.

> > The default CPU for machine=virt is arm,cortex-a15.
> >
> > Acked-by: Heinrich Schuchardt <xypron.glpk at gmx.de.
> >

Thanks.

> >>
> >> Initially, QEMU would not allow emulating these CPUs running in HYP
> >> mode (or EL2, for AArch64), but today, it also contains a complete
> >> implementation of the virtualization extensions themselves.
> >>
> >> This means we could be running U-Boot in HYP mode, in which case the
> >> LPAE long descriptor page table format is the only format that is
> >> supported. If we are not running in HYP mode, we can use either.
> >>
> >> So let's enable CONFIG_ARMV7_LPAE for qemu_arm_defconfig so that we
> >> get the best support for running with the MMU and caches enabled at
> >> any privilege level.
> >>
> >> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
>
> You missed to CC the maintainer of QEMU ARM 'VIRT' BOARD. - We have
> scripts/get_maintainer.pl to find the maintainers.
>
> Cc: Tuomas Tynkkynen <tuomas.tynkkynen at iki.fi>
>

Apologies. I will cc Tuomas for v2.