[libvirt] [PATCH v2 31/31] qemu: Store default CPU in domain XML
Ján Tomko
jtomko at redhat.com
Wed Oct 16 15:39:24 UTC 2019
On Tue, Oct 15, 2019 at 05:35:07PM +0200, Jiri Denemark wrote:
>When starting a domain without a CPU model specified in the domain XML,
>QEMU will choose a default one. Which is fine unless the domain gets
>migrated to another host because libvirt doesn't perform any CPU ABI
>checks and the virtual CPU provided by QEMU on the destination host can
>differ from the one on the source host.
>
>With QEMU 4.2.0 we can probe for the default CPU model used by QEMU for
>a particular machine type and store it in the domain XML. This way the
>chosen CPU model is more visible to users and libvirt will make sure
>the guest will see the exact same CPU after migration.
>
>Architecture specific notes
>- aarch64: We only set the default CPU for TCG domains as KVM requires
> -cpu host to work.
>
>- ppc64: (to be checked with QEMU developers) Default CPU data reported
> by QEMU is unusable for KVM. QEMU would effectively use -cpu host by
> default and it even rewrites typename of the current host CPU model to
> host-powerpc64-cpu. The default CPU type reported by query-machines is
> still power*-powerpc64-cpu, which may not even exist due to the
> changed typename. For example, on a Power8 host, power8 CPU model is
> of host-powerpc64-cpu type (according to query-cpu-definitions), while
> the default CPU type name for pseries-3.1 machine type is reported as
> power8_v2.0-powerpc64-cpu. What's even worse, pseries-4.2 says the
> default CPU type is power9_v2.0-powerpc64-cpu, which cannot be started
> on older host at all. So again, we only set the default CPU for TCG
> domains.
>
>- s390x: (to be checked with QEMU developers) The default CPU is said to
> be "qemu", which works fine for TCG domains, but it doesn't work on
> KVM because QEMU complains that some features requested in the CPU
> model are not available.
>
>- x86_64: The default CPU model (qemu64) is not runnable on any host
> with KVM, but in contrast to s390x QEMU just disables unavailable
> features and starts happily.
>
>https://bugzilla.redhat.com/show_bug.cgi?id=1598151
>https://bugzilla.redhat.com/show_bug.cgi?id=1598162
>---
>
>Notes:
> This patch should not be merged yet as we need to confirm what to do
> on s390x and ppc64 architectures.
>
> Version 2:
> - new test cases
>
> src/qemu/qemu_domain.c | 56 +++++++++++++++++++
> ...fault-cpu-tcg-virt-4.2.aarch64-latest.args | 1 +
> .../disk-cache.x86_64-latest.args | 1 +
> .../disk-cdrom-network.x86_64-latest.args | 1 +
> .../disk-cdrom-tray.x86_64-latest.args | 1 +
> .../disk-copy_on_read.x86_64-latest.args | 1 +
> .../disk-detect-zeroes.x86_64-latest.args | 1 +
> .../disk-floppy-q35-2_11.x86_64-latest.args | 1 +
> .../disk-floppy-q35-2_9.x86_64-latest.args | 1 +
> .../os-firmware-bios.x86_64-latest.args | 1 +
> ...os-firmware-efi-secboot.x86_64-latest.args | 1 +
> .../os-firmware-efi.x86_64-latest.args | 1 +
> ...ault-cpu-tcg-pseries-2.7.ppc64-latest.args | 1 +
> ...ault-cpu-tcg-pseries-3.1.ppc64-latest.args | 1 +
> ...ault-cpu-tcg-pseries-4.2.ppc64-latest.args | 1 +
> ...t-cpu-tcg-ccw-virtio-4.2.s390x-latest.args | 1 +
> .../tpm-emulator-tpm2-enc.x86_64-latest.args | 1 +
> .../tpm-emulator-tpm2.x86_64-latest.args | 1 +
> .../tpm-emulator.x86_64-latest.args | 1 +
> .../tseg-explicit-size.x86_64-latest.args | 1 +
> .../vhost-vsock-auto.x86_64-latest.args | 1 +
> .../vhost-vsock.x86_64-latest.args | 1 +
> ...-default-cpu-kvm-pc-4.2.x86_64-latest.args | 1 +
> ...default-cpu-kvm-q35-4.2.x86_64-latest.args | 1 +
> ...-default-cpu-tcg-pc-4.2.x86_64-latest.args | 1 +
> ...default-cpu-tcg-q35-4.2.x86_64-latest.args | 1 +
> ...efault-cpu-tcg-virt-4.2.aarch64-latest.xml | 3 +
> .../os-firmware-bios.x86_64-latest.xml | 3 +
> .../os-firmware-efi-secboot.x86_64-latest.xml | 3 +
> .../os-firmware-efi.x86_64-latest.xml | 3 +
> ...fault-cpu-tcg-pseries-2.7.ppc64-latest.xml | 3 +
> ...fault-cpu-tcg-pseries-3.1.ppc64-latest.xml | 3 +
> ...fault-cpu-tcg-pseries-4.2.ppc64-latest.xml | 3 +
> ...lt-cpu-tcg-ccw-virtio-4.2.s390x-latest.xml | 3 +
> .../tpm-emulator-tpm2-enc.x86_64-latest.xml | 3 +
> .../tpm-emulator-tpm2.x86_64-latest.xml | 3 +
> .../tpm-emulator.x86_64-latest.xml | 3 +
> .../tpm-passthrough-crb.x86_64-latest.xml | 3 +
> .../tpm-passthrough.x86_64-latest.xml | 3 +
> ...4-default-cpu-kvm-pc-4.2.x86_64-latest.xml | 3 +
> ...-default-cpu-kvm-q35-4.2.x86_64-latest.xml | 3 +
> ...4-default-cpu-tcg-pc-4.2.x86_64-latest.xml | 3 +
> ...-default-cpu-tcg-q35-4.2.x86_64-latest.xml | 3 +
> 43 files changed, 132 insertions(+)
>
>diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
>index 9dcba4ef38..438f003186 100644
>--- a/src/qemu/qemu_domain.c
>+++ b/src/qemu/qemu_domain.c
>@@ -4470,6 +4470,59 @@ qemuDomainDefVcpusPostParse(virDomainDefPtr def)
> }
>
>
>+static int
>+qemuDomainDefSetDefaultCPU(virDomainDefPtr def,
>+ virQEMUCapsPtr qemuCaps)
>+{
>+ VIR_AUTOPTR(virCPUDef) newCPU = NULL;
g_autoptr
>+ virCPUDefPtr cpu = def->cpu;
>+ const char *model;
>+
>+ if (cpu &&
>+ (cpu->mode != VIR_CPU_MODE_CUSTOM ||
>+ cpu->model))
>+ return 0;
>+
>+ /* Default CPU model info from QEMU is usable for TCG only on non-Intel
>+ * architectures. */
>+ if (!ARCH_IS_X86(def->os.arch) && def->virtType != VIR_DOMAIN_VIRT_QEMU)
>+ return 0;
>+
>+ model = virQEMUCapsGetMachineDefaultCPU(qemuCaps, def->os.machine, def->virtType);
>+ if (!model) {
>+ VIR_DEBUG("Unknown default CPU model for domain '%s'", def->name);
>+ return 0;
>+ }
>+
>+ VIR_DEBUG("Setting default CPU model for domain '%s' to %s",
>+ def->name, model);
>+
>+ if (!cpu) {
>+ if (VIR_ALLOC(newCPU) < 0)
>+ return -1;
>+ cpu = newCPU;
cpu = g_new0(virCPUDef, 1);
>+ }
>+
>+ /* We need to turn off all CPU checks when the domain is started because
>+ * the default CPU (e.g., qemu64) may not be runnable on any host. QEMU
>+ * will just disable the unavailable features and we will update the CPU
>+ * definition accordingly and set check to FULL when starting the domain. */
>+ cpu->type = VIR_CPU_TYPE_GUEST;
>+ cpu->mode = VIR_CPU_MODE_CUSTOM;
>+ cpu->match = VIR_CPU_MATCH_EXACT;
>+ cpu->check = VIR_CPU_CHECK_NONE;
>+ cpu->fallback = VIR_CPU_FALLBACK_FORBID;
>+
>+ if (VIR_STRDUP(cpu->model, model) < 0)
>+ return -1;
g_strdup
>+
>+ if (newCPU)
>+ VIR_STEAL_PTR(def->cpu, newCPU);
g_strdup_pointer, or just don't steal it and use def->cpu directly
>+
>+ return 0;
>+}
>+
>+
> static int
> qemuDomainDefCPUPostParse(virDomainDefPtr def)
> {
Jano
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