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Re: [PATCH 2/2] hw/intc: Have ARM_GIC select ARM_GICV3 when KVM is not a


From: Phil Dennis-Jordan
Subject: Re: [PATCH 2/2] hw/intc: Have ARM_GIC select ARM_GICV3 when KVM is not available
Date: Tue, 7 Jan 2025 17:05:48 +0100



On Sat, 28 Dec 2024 at 11:48, Phil Dennis-Jordan <phil@philjordan.eu> wrote:


On Fri, 27 Dec 2024 at 21:24, Philippe Mathieu-Daudé <philmd@linaro.org> wrote:
When the KVM accelerator is selected, the Kconfig ARM_GIC key
selects the KVM GIC implementation (ARM_GIC_KVM).
For other accelerators (TCG, HVF, ...), select the generic
implementation.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 hw/intc/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/intc/Kconfig b/hw/intc/Kconfig
index 7547528f2c2..762139d8df3 100644
--- a/hw/intc/Kconfig
+++ b/hw/intc/Kconfig
@@ -23,7 +23,7 @@ config APIC

 config ARM_GIC
     bool
-    select ARM_GICV3 if TCG
+    select ARM_GICV3 if !KVM

Wouldn't this disable the ARM_GICV3 by default when building with --enable-tcg --enable-kvm? And then there would be no GIC available when running the built QEMU in TCG mode. (Bear with me, I'm a relative Meson newbie.)
 


OK, I've managed to answer my own question now by setting up a RPi5 with aarch64 RPOS and building QEMU on that with --enable-kvm --enable-tcg. With patch 1/2 applied on current upstream master, I get:

$ build/qemu-system-aarch64 -accel tcg -M virt,gic-version=3 -smp 4 -m 4G
[runs successfully]

with 2/2 applied as well:

$ build/qemu-system-aarch64 -accel tcg -M virt,gic-version=3 -smp 4 -m 4G
qemu-system-aarch64: tcg does not support GICv3 emulation
$

In other words, with the proposed change, ARM_GICV3 is indeed deselected if KVM is selected even if TCG is also selected.


Possibly very basic question: is there any support for kernel-irqchip=off on aarch64/KVM?
If yes, don't we need ARM_GICV3 in that case anyway, so we should drop any accel dependency on it in the first place?


If we definitely don't need the software GIC in KVM-only builds, I guess we're down to listing each accel that needs it individually. Is that:

select ARM_GICV3 if TCG || HVF || NVMM || WHPX || XEN_EMU || XEN

or can we drop any of those? Have I missed anything? What about QTest?


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