Re: [libvirt] [PATCH 3/5] qemu: Use GICv2 for aarch64/virt TCG guests

There are currently some limitations in the emulated GICv3 that make it unsuitable as a default. Use GICv2 instead. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1450433 Signed-off-by: Andrea Bolognani <abologna(a)redhat.com&gt; --- src/qemu/qemu_domain.c | 41 +++++++++++++++------- .../qemuxml2argv-aarch64-gic-none-tcg.args | 2 +- .../qemuxml2xmlout-aarch64-gic-none-tcg.xml | 2 +- 3 files changed, 31 insertions(+), 14 deletions(-) diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c index cc02c80..31ed391 100644 --- a/src/qemu/qemu_domain.c +++ b/src/qemu/qemu_domain.c @@ -2559,17 +2559,31 @@ qemuDomainDefEnableDefaultFeatures(virDomainDefPtr def, if (def->features[VIR_DOMAIN_FEATURE_GIC] == VIR_TRISTATE_SWITCH_ABSENT && qemuDomainIsVirt(def)) { - VIR_DEBUG("Looking for usable GIC version in domain capabilities"); - for (version = VIR_GIC_VERSION_LAST - 1; - version > VIR_GIC_VERSION_NONE; - version--) { - if (virQEMUCapsSupportsGICVersion(qemuCaps, - def->virtType, - version)) { - VIR_DEBUG("Using GIC version %s", - virGICVersionTypeToString(version)); - def->gic_version = version; - break; + /* We want to use the highest available GIC version for guests; + * however, the emulated GICv3 is currently lacking a MSI controller, + * making it unsuitable for the pure PCIe topology we aim for. + * + * For that reason, we skip this step entirely for TCG guests, + * and rely on the code below to pick the default version, GICv2, + * which supports all the features we need. + * + * We'll want to revisit this once MSI support for GICv3 has been + * implemented in QEMU. + * + * See https://bugzilla.redhat.com/show_bug.cgi?id=1414081 */ + if (def->virtType == VIR_DOMAIN_VIRT_KVM) {

+ VIR_DEBUG("Looking for usable GIC version in domain capabilities"); + for (version = VIR_GIC_VERSION_LAST - 1; + version > VIR_GIC_VERSION_NONE; + version--) { + if (virQEMUCapsSupportsGICVersion(qemuCaps, + def->virtType, + version)) { + VIR_DEBUG("Using GIC version %s", + virGICVersionTypeToString(version)); + def->gic_version = version; + break; + } } }