On 30.06.19 00:42, Marc Zyngier wrote:
On Sat, 29 Jun 2019 19:09:37 +0200
Jan Kiszka <jan.kiszka@xxxxxx> 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! ;-)
Optimistic.
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.
You mean something like KVM_ARM_TARGET_GENERIC_V8? Need to study that...
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.
Probably just in their DT. How can I check if the maintenance IRQ is working?
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...
I played with compiling the rpi kernel for 64-bit. Lots of pieces from the
graphic drivers are falling from the truck, but you can make it build at least.
Not that it boots so far or gives any early messages. Probably that is the reason:
https://github.com/raspberrypi/linux/issues/3032
Jan
