Re: [PATCH] qemu: Enable I/O APIC if needed
On 12/12/24 12:37, Ján Tomko wrote:
On a Thursday in 2024, Michal Privoznik wrote:
> This is a follow up of my previous commits. If the number of
> vCPUs exceeds some arbitrary value (255) then QEMU requires IOMMU
> with EIM and interemap enabled. But in turn, intremap IOMMU
s/interemap/intremap/
> requires split I/O APIC (per virDomainDefIOMMUValidate()). Since
> after my previous commits (e.g. v10.10.0-rc1~183) IOMMU is added
> automagically, the I/O APIC can be also enabled automagically.
>
> Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com>
> ---
> src/qemu/qemu_postparse.c | 7 +++++++
> tests/qemuxmlconfdata/intel-iommu-eim-autoadd.xml | 3 ---
> 2 files changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/src/qemu/qemu_postparse.c b/src/qemu/qemu_postparse.c
> index 03b5ef825a..f48f172c37 100644
> --- a/src/qemu/qemu_postparse.c
> +++ b/src/qemu/qemu_postparse.c
> @@ -1547,6 +1547,13 @@ qemuDomainDefEnableDefaultFeatures(virDomainDef
> *def,
> * capabilities, we still want to enable this */
> def->features[VIR_DOMAIN_FEATURE_GIC] = VIR_TRISTATE_SWITCH_ON;
> }
> +
> + /* IOMMU with intremap requires split I/O APIC */
The error message in hw/i386/x86-iommu.c suggests otherwise:
/* Both Intel and AMD IOMMU IR only support "kernel-irqchip={off|
split}" */
if (x86_iommu_ir_supported(x86_iommu) && irq_all_kernel) {
error_setg(errp, "Interrupt Remapping cannot work with "
"kernel-irqchip=on, please use
'split|off'.");
return;
}
Does it?
./qemu-system-x86_64 \
-machine q35,acpi=off \
-accel kvm \
-cpu qemu64 \
-m size=219136k \
-smp 288,sockets=288,cores=1,threads=1 \
-display none \
-no-user-config \
-nodefaults \
-device
'{"driver":"intel-iommu","id":"iommu0","intremap":"on","eim":"on"}'
qemu-system-x86_64: -device
{"driver":"intel-iommu","id":"iommu0","intremap":"on","eim":"on"}:
Interrupt Remapping cannot work with kernel-irqchip=on, please use
'split|off'.
whereas:
./qemu-system-x86_64 \
-machine q35,acpi=off,kernel_irqchip=split \
-accel kvm \
-cpu qemu64 \
-m size=219136k \
-smp 288,sockets=288,cores=1,threads=1 \
-display none \
-no-user-config \
-nodefaults \
-device
'{"driver":"intel-iommu","id":"iommu0","intremap":"on","eim":"on"}'
starts just fine (modulo warnings that the number of vCPUs exceeds the
number of physical CPUs, but that's irrelevant for this debate).
> + if (def->iommu &&
> + def->iommu->intremap == VIR_TRISTATE_SWITCH_ON &&
> + def->features[VIR_DOMAIN_FEATURE_IOAPIC] ==
> VIR_DOMAIN_IOAPIC_NONE) {
> + def->features[VIR_DOMAIN_FEATURE_IOAPIC] =
> VIR_DOMAIN_IOAPIC_QEMU;
> + }
This should be only done if the IOMMU was auto-added, to not override it
for user-specified IOMMU.
I'm not sure about that. Consider the following XML:
<domain type='kvm'>
<name>QEMUGuest1</name>
<memory unit='KiB'>219100</memory>
<currentMemory unit='KiB'>219100</currentMemory>
<vcpu placement='static'>2</vcpu>
<os>
<type arch='x86_64' machine='q35'>hvm</type>
<boot dev='hd'/>
</os>
<devices>
<emulator>/usr/bin/qemu-system-x86_64</emulator>
<iommu model='intel'>
<driver intremap='on' eim='on'/>
</iommu>
</devices>
</domain>
The number of vCPUs is well within the limit and the XML contains IOMMU,
yet, creating the domain fails:
error: unsupported configuration: IOMMU interrupt remapping requires
split I/O APIC (ioapic driver='qemu')
Michal