| From ccda4494b0ea4b81b6b0c3e539a0bcf7e673c68c Mon Sep 17 00:00:00 2001 |
| From: Eduardo Habkost <ehabkost@redhat.com> |
| Date: Thu, 5 Dec 2019 21:56:50 +0000 |
| Subject: [PATCH 01/18] i386: Resolve CPU models to v1 by default |
| |
| RH-Author: Eduardo Habkost <ehabkost@redhat.com> |
| Message-id: <20191205225650.772600-2-ehabkost@redhat.com> |
| Patchwork-id: 92907 |
| O-Subject: [RHEL-AV-8.1.1 qemu-kvm PATCH 1/1] i386: Resolve CPU models to v1 by default |
| Bugzilla: 1787291 1779078 1779078 |
| RH-Acked-by: Danilo de Paula <ddepaula@redhat.com> |
| RH-Acked-by: Igor Mammedov <imammedo@redhat.com> |
| RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com> |
| |
| Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1779078 |
| Brew: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=25187823 |
| Upstream: submitted, Message-Id: <20191205223339.764534-1-ehabkost@redhat.com> |
| |
| When using `query-cpu-definitions` using `-machine none`, |
| QEMU is resolving all CPU models to their latest versions. The |
| actual CPU model version being used by another machine type (e.g. |
| `pc-q35-4.0`) might be different. |
| |
| In theory, this was OK because the correct CPU model |
| version is returned when using the correct `-machine` argument. |
| |
| Except that in practice, this breaks libvirt expectations: |
| libvirt always use `-machine none` when checking if a CPU model |
| is runnable, because runnability is not expected to be affected |
| when the machine type is changed. |
| |
| For example, when running on a Haswell host without TSX, |
| Haswell-v4 is runnable, but Haswell-v1 is not. On those hosts, |
| `query-cpu-definitions` says Haswell is runnable if using |
| `-machine none`, but Haswell is actually not runnable using any |
| of the `pc-*` machine types (because they resolve Haswell to |
| Haswell-v1). In other words, we're breaking the "runnability |
| guarantee" we promised to not break for a few releases (see |
| qemu-deprecated.texi). |
| |
| To address this issue, change the default CPU model version to v1 |
| on all machine types, so we make `query-cpu-definitions` output |
| when using `-machine none` match the results when using `pc-*`. |
| This will change in the future (the plan is to always return the |
| latest CPU model version if using `-machine none`), but only |
| after giving libvirt the opportunity to adapt. |
| |
| Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1779078 |
| Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> |
| Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com> |
| |
| qemu-deprecated.texi | 7 +++++++ |
| target/i386/cpu.c | 8 +++++++- |
| 2 files changed, 14 insertions(+), 1 deletion(-) |
| |
| diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi |
| index 4b4b742..534ebe9 100644 |
| |
| |
| @@ -374,6 +374,13 @@ guarantees must resolve the CPU model aliases using te |
| ``alias-of'' field returned by the ``query-cpu-definitions'' QMP |
| command. |
| |
| +While those guarantees are kept, the return value of |
| +``query-cpu-definitions'' will have existing CPU model aliases |
| +point to a version that doesn't break runnability guarantees |
| +(specifically, version 1 of those CPU models). In future QEMU |
| +versions, aliases will point to newer CPU model versions |
| +depending on the machine type, so management software must |
| +resolve CPU model aliases before starting a virtual machine. |
| |
| @node Recently removed features |
| @appendix Recently removed features |
| diff --git a/target/i386/cpu.c b/target/i386/cpu.c |
| index 6dce6f2..863192c 100644 |
| |
| |
| @@ -3926,7 +3926,13 @@ static PropValue tcg_default_props[] = { |
| }; |
| |
| |
| -X86CPUVersion default_cpu_version = CPU_VERSION_LATEST; |
| +/* |
| + * We resolve CPU model aliases using -v1 when using "-machine |
| + * none", but this is just for compatibility while libvirt isn't |
| + * adapted to resolve CPU model versions before creating VMs. |
| + * See "Runnability guarantee of CPU models" at * qemu-deprecated.texi. |
| + */ |
| +X86CPUVersion default_cpu_version = 1; |
| |
| void x86_cpu_set_default_version(X86CPUVersion version) |
| { |
| -- |
| 1.8.3.1 |
| |