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

[Heinrich Schuchardt]

Am June 7, 2020 8:59:00 AM UTC schrieb Ard Biesheuvel <ardb at kernel.org>:
>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.

By missing feature I meant  -cpu help output should be filtered according to the -machine value if provided.

>
>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.