On Sat, 29 Jun 2019 19:09:37 +0200
Jan Kiszka <[email protected]> wrote:
Hi Jan,
> Hi all,
>
> just got KVM running on the Raspberry Pi4. Seems they now embedded all
> required logic into that new SoC.
Yeah, someone saw the light and decided to enter the 21st century by
attaching a GICv2 to the thing. Who knows, they may plug a GICv3 and a
SMMU in 2050 at that rate! ;-)
> However, as the Raspberry kernel is not yet ready for 64-bit (and
> upstream is not in sight), I had to use legacy 32-bit mode. And there we
> stumble over the core detection. This little patch made it work, though:
>
> diff --git a/arch/arm/kvm/guest.c b/arch/arm/kvm/guest.c
> index 2b8de885b2bf..01606aad73cc 100644
> --- a/arch/arm/kvm/guest.c
> +++ b/arch/arm/kvm/guest.c
> @@ -290,6 +290,7 @@ int __attribute_const__ kvm_target_cpu(void)
> case ARM_CPU_PART_CORTEX_A7:
> return KVM_ARM_TARGET_CORTEX_A7;
> case ARM_CPU_PART_CORTEX_A15:
> + case ARM_CPU_PART_CORTEX_A72:
> return KVM_ARM_TARGET_CORTEX_A15;
> default:
> return -EINVAL;
>
> That raises the question if this is hack or a valid change and if there
> is general interest in mapping 64-bit cores on 32-bit if they happen to
> run in 32-bit mode.
The real thing to do here would be to move to a generic target, much
like we did on the 64bit side. Could you investigate that instead? It
would also allow KVM to be used on other 32bit cores such as
A12/A17/A32.
Although some would argue that the *real* real thing to do would be "rm
-rf arch/arm/kvm" and be done with it, but that's a discussion for next
week... ;-)
> Jan
>
> PS: The RPi device tree lacks description of the GICH maintenance
> interrupts. Seems KVM is fine without that - because it has the
> information hard-coded or because it can live without that interrupt?
Nah, it really should have an interrupt here. You can end-up in
situation where new virtual interrupts are delayed until the next
natural exit if you don't get a maintenance interrupt. Feels like a bug.
Anyway, if you know of any effort to get a 64bit kernel on that thing,
I'm interested in helping. I bought one on Monday, but didn't get a
change to do any hacking on it just yet...
Thanks,
M.
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