diff --git a/i386-Resolve-CPU-models-to-v1-by-default.patch b/i386-Resolve-CPU-models-to-v1-by-default.patch new file mode 100644 index 0000000..f8c6315 --- /dev/null +++ b/i386-Resolve-CPU-models-to-v1-by-default.patch @@ -0,0 +1,81 @@ +From 6a5e994c1dec959143f6d3f83169a7adcb173fc4 Mon Sep 17 00:00:00 2001 +From: Eduardo Habkost +Date: Thu, 5 Dec 2019 19:33:39 -0300 +Subject: [PATCH] i386: Resolve CPU models to v1 by default + +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 +Message-Id: <20191205223339.764534-1-ehabkost@redhat.com> +Signed-off-by: Eduardo Habkost +--- + qemu-deprecated.texi | 8 ++++++++ + target/i386/cpu.c | 8 +++++++- + 2 files changed, 15 insertions(+), 1 deletion(-) + +diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi +index fff07bb2a3..719ac23d72 100644 +--- a/qemu-deprecated.texi ++++ b/qemu-deprecated.texi +@@ -331,3 +331,11 @@ existing CPU models. Management software that needs runnability + 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. +diff --git a/target/i386/cpu.c b/target/i386/cpu.c +index e0f3a2dd99..22e0e89718 100644 +--- a/target/i386/cpu.c ++++ b/target/i386/cpu.c +@@ -3933,7 +3933,13 @@ 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) + { +-- +2.27.0 +