On Wed, Mar 5, 2025 at 3:53 AM Ani Sinha <anisi...@redhat.com> wrote:
>
> On Fri, Jan 31, 2025 at 3:24 PM Igor Mammedov <imamm...@redhat.com> wrote:
> >
> > On Tue, 28 Jan 2025 09:25:26 +0530
> > Ani Sinha <anisi...@redhat.com> wrote:
> >
> > > commit 0788a56bd1ae3 ("i386: Make unversioned CPU models be aliases")
> > > introduced 'default_cpu_version' for PCMachineClass. This created three
> > > categories of CPU models:
> > > - Most unversioned CPU models would use version 1 by default.
> > > - For machines 4.0.1 and older that do not support cpu model aliases, a
> > > special default_cpu_version value of CPU_VERSION_LEGACY is used.
> > > - It was thought that future machines would use the latest value of cpu
> > > versions corresponding to default_cpu_version value of
> > > CPU_VERSION_LATEST [1].
> > >
> > > All pc machines still use the default cpu version of 1 for
> > > unversioned cpu models. CPU_VERSION_LATEST is a moving target and
> > > changes with time. Therefore, if machines use CPU_VERSION_LATEST, it would
> > > mean that over a period of time, for the same machine type, the cpu
> > > version
> > > would be different depending on what is latest at that time. This would
> > > break guests even when they use a versioned machine type. Therefore, for
> > > pc machines, use of CPU_VERSION_LATEST is not possible. Currently, only
> > > microvms use CPU_VERSION_LATEST.
> > >
> > > This change cleans up the complicated logic around default_cpu_version
> > > including getting rid of default_cpu_version property itself. A couple of
> > > new
> > > flags are introduced, one for the legacy model for machines 4.0.1 and
> > > older
> > > and other for microvms. For older machines, a new pc machine property is
> > > introduced that separates pc machine versions 4.0.1 and older from the
> > > newer
> > > machines. 4.0.1 and older machines are scheduled to be deleted towards
> > > end of 2025 since they would be 6 years old by then. At that time, we can
> > > remove all logic around legacy cpus. Microvms are the only machines that
> > > continue to use the latest cpu version. If this changes later, we can
> > > remove all logic around x86_cpu_model_last_version(). Default cpu version
> > > for unversioned cpu models is hardcoded to the value 1 and applies
> > > unconditionally for all pc machine types of version 4.1 and above.
> > >
> > > This change also removes all complications around CPU_VERSION_AUTO
> > > including removal of the value itself.
> > >
> > > 1) See commit dcafd1ef0af227 ("i386: Register versioned CPU models")
> > >
> > > CC: imamm...@redhat.com
> > > Signed-off-by: Ani Sinha <anisi...@redhat.com>
> > > Reviewed-by: Zhao Liu <zhao1....@intel.com>
> > > ---
> > > hw/i386/microvm.c | 3 +-
> > > hw/i386/pc.c | 14 +++++++++
> > > hw/i386/pc_piix.c | 6 ++--
> > > hw/i386/pc_q35.c | 6 ++--
> > > hw/i386/x86-common.c | 4 +--
> > > include/hw/i386/pc.h | 7 +++--
> > > include/hw/i386/x86.h | 2 +-
> > > target/i386/cpu.c | 69 ++++++++++++++++++++++---------------------
> > > target/i386/cpu.h | 21 +++----------
> > > 9 files changed, 67 insertions(+), 65 deletions(-)
> > >
> > > changelog:
> > > v2: explain in commit log why use of CPU_VERSION_LATEST for machines
> > > is problematic.
> > > v3: fix a bug that broke the pipeline
> > > https://gitlab.com/mstredhat/qemu/-/pipelines/1626171267
> > > when cpu versions are explicitly specified in the command line,
> > > respect that and do not enforce legacy (unversioned) cpu logic.
> > > The pipeline is green now with the fix:
> > > https://gitlab.com/anisinha/qemu/-/pipelines/1626783632
> > > v4: made changes as per Zhao's suggestions.
> > > Pipeline passes https://gitlab.com/anisinha/qemu/-/pipelines/1635829877
> > > v5: adjustment of pc_init_cpus() declaration as per Zhao's suggestion.
> > > This
> > > simplifies things and also passes compilation.
> > > CI still passes https://gitlab.com/anisinha/qemu/-/pipelines/1637657451
> > > v6: cosmetic commit log correction as suggested by Igor. rebase, added
> > > tags.
> > >
> > > diff --git a/hw/i386/microvm.c b/hw/i386/microvm.c
> > > index a8d354aabe..ffb1b37fe5 100644
> > > --- a/hw/i386/microvm.c
> > > +++ b/hw/i386/microvm.c
> > > @@ -458,7 +458,8 @@ static void microvm_machine_state_init(MachineState
> > > *machine)
> > >
> > > microvm_memory_init(mms);
> > >
> > > - x86_cpus_init(x86ms, CPU_VERSION_LATEST);
> > > + x86_cpu_uses_lastest_version();
> >
> > for microvm, we do not have versioned machines,
> > hence we are not obliged to keep the same cpu between
> > different qemu versions.
> >
> > I'd prefer to follow arm/virt with no default cpu behavior,
> > but that ship has sailed off already.
> >
> > Lets try instead of the latest, use cpu model name as is
> > (i.e. typically it would be non versioned model) that would keep
> > existing CLI work.
> > Ones that want a specific version can use explicit versioned name on CLI.
> >
> > i.e. remove the notion of CPU_VERSION_LATEST 1st (a separate patch).
> > if this accepted that would make this patch a bit simpler.
> >
> > > + x86_cpus_init(x86ms);
> > >
> > > microvm_devices_init(mms);
> > > }
> > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > > index b46975c8a4..f97a519573 100644
> > > --- a/hw/i386/pc.c
> > > +++ b/hw/i386/pc.c
> > > @@ -30,6 +30,7 @@
> > > #include "hw/hyperv/hv-balloon.h"
> > > #include "hw/i386/fw_cfg.h"
> > > #include "hw/i386/vmport.h"
> > > +#include "target/i386/cpu.h"
> > > #include "system/cpus.h"
> > > #include "hw/ide/ide-bus.h"
> > > #include "hw/timer/hpet.h"
> > > @@ -615,6 +616,19 @@ void pc_acpi_smi_interrupt(void *opaque, int irq,
> > > int level)
> > > }
> > > }
> > >
> > > +void pc_init_cpus(MachineState *ms)
> > > +{
> > I'd not introduce this function, instead add duplicated
> > call x86_cpu_set_legacy_version() to pc_init1/pc_q35_init,
> > this way it would be more concise and introduce less code churn
> >
> > > + X86MachineState *x86ms = X86_MACHINE(ms);
> > > + PCMachineState *pcms = PC_MACHINE(ms);
> > > + PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
> > > +
> > > + if (pcmc->no_versioned_cpu_model) {
> > > + /* use legacy cpu as it does not support versions */
> > > + x86_cpu_set_legacy_version();
> > > + }
> > > + x86_cpus_init(x86ms);
> > > +}
> > > +
> > > static
> > > void pc_machine_done(Notifier *notifier, void *data)
> > > {
> > > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> > > index 04d2957adc..dc684cb011 100644
> > > --- a/hw/i386/pc_piix.c
> > > +++ b/hw/i386/pc_piix.c
> > > @@ -181,7 +181,8 @@ static void pc_init1(MachineState *machine, const
> > > char *pci_type)
> > > }
> > >
> > > pc_machine_init_sgx_epc(pcms);
> > > - x86_cpus_init(x86ms, pcmc->default_cpu_version);
> > > +
> > > + pc_init_cpus(machine);
> > >
> > > if (kvm_enabled()) {
> > > kvmclock_create(pcmc->kvmclock_create_always);
> > > @@ -457,7 +458,6 @@ static void pc_i440fx_machine_options(MachineClass *m)
> > > ObjectClass *oc = OBJECT_CLASS(m);
> > > pcmc->default_south_bridge = TYPE_PIIX3_DEVICE;
> > > pcmc->pci_root_uid = 0;
> > > - pcmc->default_cpu_version = 1;
> > >
> > > m->family = "pc_piix";
> > > m->desc = "Standard PC (i440FX + PIIX, 1996)";
> > > @@ -669,7 +669,7 @@ static void
> > > pc_i440fx_machine_4_0_options(MachineClass *m)
> > > {
> > > PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
> > > pc_i440fx_machine_4_1_options(m);
> > > - pcmc->default_cpu_version = CPU_VERSION_LEGACY;
> > > + pcmc->no_versioned_cpu_model = true;
> > > compat_props_add(m->compat_props, hw_compat_4_0, hw_compat_4_0_len);
> > > compat_props_add(m->compat_props, pc_compat_4_0, pc_compat_4_0_len);
> > > }
> > > diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> > > index 77536dd697..045b05da64 100644
> > > --- a/hw/i386/pc_q35.c
> > > +++ b/hw/i386/pc_q35.c
> > > @@ -187,7 +187,8 @@ static void pc_q35_init(MachineState *machine)
> > > }
> > >
> > > pc_machine_init_sgx_epc(pcms);
> > > - x86_cpus_init(x86ms, pcmc->default_cpu_version);
> > > +
> > I'd drop newline
> >
> > > + pc_init_cpus(machine);
> > >
> > > if (kvm_enabled()) {
> > > kvmclock_create(pcmc->kvmclock_create_always);
> > > @@ -339,7 +340,6 @@ static void pc_q35_machine_options(MachineClass *m)
> > > {
> > > PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
> > > pcmc->pci_root_uid = 0;
> > > - pcmc->default_cpu_version = 1;
> > >
> > > m->family = "pc_q35";
> > > m->desc = "Standard PC (Q35 + ICH9, 2009)";
> > > @@ -547,7 +547,7 @@ static void pc_q35_machine_4_0_1_options(MachineClass
> > > *m)
> > > {
> > > PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
> > > pc_q35_machine_4_1_options(m);
> > > - pcmc->default_cpu_version = CPU_VERSION_LEGACY;
> > > + pcmc->no_versioned_cpu_model = true;
> > > /*
> > > * This is the default machine for the 4.0-stable branch. It is
> > > basically
> > > * a 4.0 that doesn't use split irqchip by default. It MUST hence
> > > apply the
> > > diff --git a/hw/i386/x86-common.c b/hw/i386/x86-common.c
> > > index 008496b5b8..1ed5bc6010 100644
> > > --- a/hw/i386/x86-common.c
> > > +++ b/hw/i386/x86-common.c
> > > @@ -66,15 +66,13 @@ out:
> > > object_unref(cpu);
> > > }
> > >
> > > -void x86_cpus_init(X86MachineState *x86ms, int default_cpu_version)
> > > +void x86_cpus_init(X86MachineState *x86ms)
> > > {
> > > int i;
> > > const CPUArchIdList *possible_cpus;
> > > MachineState *ms = MACHINE(x86ms);
> > > MachineClass *mc = MACHINE_GET_CLASS(x86ms);
> > >
> > > - x86_cpu_set_default_version(default_cpu_version);
> > > -
> > > /*
> > > * Calculates the limit to CPU APIC ID values
> > > *
> > > diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> > > index a558705cb9..563f765d7f 100644
> > > --- a/include/hw/i386/pc.h
> > > +++ b/include/hw/i386/pc.h
> > > @@ -92,9 +92,6 @@ struct PCMachineClass {
> > >
> > > /* Compat options: */
> > >
> > > - /* Default CPU model version. See x86_cpu_set_default_version(). */
> > > - int default_cpu_version;
> > > -
> > > /* ACPI compat: */
> > > bool has_acpi_build;
> > > int pci_root_uid;
> > > @@ -125,6 +122,9 @@ struct PCMachineClass {
> > > * check for memory.
> > > */
> > > bool broken_32bit_mem_addr_check;
> > > +
> > > + /* whether the machine supports versioned cpu models */
> > > + bool no_versioned_cpu_model;
> > > };
> > >
> > > #define TYPE_PC_MACHINE "generic-pc-machine"
> > > @@ -136,6 +136,7 @@ GSIState *pc_gsi_create(qemu_irq **irqs, bool
> > > pci_enabled);
> > >
> > > /* pc.c */
> > >
> > > +void pc_init_cpus(MachineState *ms);
> > > void pc_acpi_smi_interrupt(void *opaque, int irq, int level);
> > >
> > > #define PCI_HOST_PROP_RAM_MEM "ram-mem"
> > > diff --git a/include/hw/i386/x86.h b/include/hw/i386/x86.h
> > > index d43cb3908e..2d2b987fa1 100644
> > > --- a/include/hw/i386/x86.h
> > > +++ b/include/hw/i386/x86.h
> > > @@ -114,7 +114,7 @@ void init_topo_info(X86CPUTopoInfo *topo_info, const
> > > X86MachineState *x86ms);
> > > uint32_t x86_cpu_apic_id_from_index(X86MachineState *x86ms,
> > > unsigned int cpu_index);
> > >
> > > -void x86_cpus_init(X86MachineState *pcms, int default_cpu_version);
> > > +void x86_cpus_init(X86MachineState *pcms);
> > > void x86_rtc_set_cpus_count(ISADevice *rtc, uint16_t cpus_count);
> > > void x86_cpu_pre_plug(HotplugHandler *hotplug_dev,
> > > DeviceState *dev, Error **errp);
> > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > > index 1b9c11022c..c1f868c4dd 100644
> > > --- a/target/i386/cpu.c
> > > +++ b/target/i386/cpu.c
> > > @@ -192,6 +192,9 @@ struct CPUID2CacheDescriptorInfo
> > > cpuid2_cache_descriptors[] = {
> > > */
> > > #define CACHE_DESCRIPTOR_UNAVAILABLE 0xFF
> > >
> > > +/* default cpu version to use */
> > > +#define DEFAULT_CPU_VERSION 1
> > > +
> > > /*
> > > * Return a CPUID 2 cache descriptor for a given cache.
> > > * If no known descriptor is found, return CACHE_DESCRIPTOR_UNAVAILABLE
> > > @@ -5343,20 +5346,16 @@ static const X86CPUDefinition builtin_x86_defs[]
> > > = {
> > > },
> > > };
> > >
> > > -/*
> > > - * 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
> > > - * docs/about/deprecated.rst.
> > > - */
> > > -X86CPUVersion default_cpu_version = 1;
> > > +static bool use_legacy_cpu;
> > > +void x86_cpu_set_legacy_version(void)
> > > +{
> > > + use_legacy_cpu = true;
> > so all the difference between legacy and not legacy, is alias_of
> > in QMP output.
> >
> > In that case lets be more specific and name it as such
> > i.e. something like 'qmp_has_alias'
> >
> > > +}
> > >
> > > -void x86_cpu_set_default_version(X86CPUVersion version)
> > > +static bool use_latest_cpu;
> > > +void x86_cpu_uses_lastest_version(void)
> > > {
> > > - /* Translating CPU_VERSION_AUTO to CPU_VERSION_AUTO doesn't make
> > > sense */
> > > - assert(version != CPU_VERSION_AUTO);
> > > - default_cpu_version = version;
> > > + use_latest_cpu = true;
> > > }
> > >
> > > static X86CPUVersion x86_cpu_model_last_version(const X86CPUModel *model)
> > > @@ -5374,14 +5373,11 @@ static X86CPUVersion
> > > x86_cpu_model_last_version(const X86CPUModel *model)
> > > /* Return the actual version being used for a specific CPU model */
> > > static X86CPUVersion x86_cpu_model_resolve_version(const X86CPUModel
> > > *model)
> > > {
> > > - X86CPUVersion v = model->version;
> > > - if (v == CPU_VERSION_AUTO) {
> > > - v = default_cpu_version;
> > > - }
> > > - if (v == CPU_VERSION_LATEST) {
> > > + if (use_latest_cpu) {
> > > return x86_cpu_model_last_version(model);
> > > }
> > > - return v;
> > > +
> > I'd drop newline
> >
> > > + return model->version;
> > > }
> > >
> > > static const Property max_x86_cpu_properties[] = {
> > > @@ -5985,10 +5981,15 @@ static char
> > > *x86_cpu_class_get_alias_of(X86CPUClass *cc)
> > > if (!cc->model || !cc->model->is_alias) {
> > > return NULL;
> > > }
> > > - version = x86_cpu_model_resolve_version(cc->model);
> > > - if (version <= 0) {
> > > +
> > > + if (use_legacy_cpu) {
> > > + /* legacy cpu models do not support cpu aliases */
> > > return NULL;
> > > }
> > > +
> > > + version = x86_cpu_model_resolve_version(cc->model);
> > > + assert(version);
> > > +
> > > return x86_cpu_versioned_model_name(cc->model->cpudef, version);
> > > }
> > >
> > > @@ -6002,11 +6003,7 @@ static void x86_cpu_list_entry(gpointer data,
> > > gpointer user_data)
> > > g_autofree char *model_id = x86_cpu_class_get_model_id(cc);
> > >
> > > if (!desc && alias_of) {
> > > - if (cc->model && cc->model->version == CPU_VERSION_AUTO) {
> > > - desc = g_strdup("(alias configured by machine type)");
> > > - } else {
> > > desc = g_strdup_printf("(alias of %s)", alias_of);
> > misaligned wrt 'new' 'if' block?
> >
> > > - }
> > > }
> > > if (!desc && cc->model && cc->model->note) {
> > > desc = g_strdup_printf("%s [%s]", model_id, cc->model->note);
> > > @@ -6109,13 +6106,8 @@ static void x86_cpu_definition_entry(gpointer
> > > data, gpointer user_data)
> > > } else {
> > > info->deprecated = false;
> > > }
> > > - /*
> > > - * Old machine types won't report aliases, so that alias translation
> > > - * doesn't break compatibility with previous QEMU versions.
> > > - */
> > > - if (default_cpu_version != CPU_VERSION_LEGACY) {
> > > - info->alias_of = x86_cpu_class_get_alias_of(cc);
> > > - }
> > > +
> > > + info->alias_of = x86_cpu_class_get_alias_of(cc);
> > >
> > > QAPI_LIST_PREPEND(*cpu_list, info);
> > > }
> > > @@ -6287,7 +6279,12 @@ static void x86_cpu_apply_version_props(X86CPU
> > > *cpu, X86CPUModel *model)
> > > const X86CPUVersionDefinition *vdef;
> > > X86CPUVersion version = x86_cpu_model_resolve_version(model);
> > >
> > > - if (version == CPU_VERSION_LEGACY) {
> > > + /*
> > > + * if the machine uses legacy cpus, use legacy cpus with no versions
> > > + * when no explict CPU versions are specified in the CPU definition
> > > + * passed from the command line.
> > > + */
> > > + if (version == DEFAULT_CPU_VERSION && use_legacy_cpu) {
> > > return;
> > > }
> >
> > I think we can safely drop this check altogether since followup
> > call x86_cpu_def_get_versions will return version 1 if not specified
> > and looking at model definitions all existing v1 defs have no property
> > overrides. So 'for' loop is effectively would be nop.
>
> See this https://lists.gnu.org/archive/html/qemu-devel/2025-01/msg02559.html
> I think this check is needed otherwise
> tests/functional/test_x86_cpu_model_versions.py fails. You can analyze
> why.
I take this back, That bugfix was different. The conditional in its
current form is redundant.
Removed it and it passed CI
https://gitlab.com/anisinha/qemu/-/pipelines/1700325177.
>
> >
> > >
> > > @@ -6317,7 +6314,11 @@ static const CPUCaches
> > > *x86_cpu_get_versioned_cache_info(X86CPU *cpu,
> > > X86CPUVersion version = x86_cpu_model_resolve_version(model);
> > > const CPUCaches *cache_info = model->cpudef->cache_info;
> > >
> > > - if (version == CPU_VERSION_LEGACY) {
> > > + /*
> > > + * If machine supports legacy cpus and no explicit cpu versions are
> > > + * specified, use the cache from the unversioned cpu definition.
> > > + */
> > > + if (version == DEFAULT_CPU_VERSION && use_legacy_cpu) {
> > > return cache_info;
> > > }
> >
> > the same as above comment, only wrt cache_info
> >
> > >
> > > @@ -6452,7 +6453,7 @@ static void x86_register_cpudef_types(const
> > > X86CPUDefinition *def)
> > > /* Unversioned model: */
> > > m = g_new0(X86CPUModel, 1);
> > > m->cpudef = def;
> > > - m->version = CPU_VERSION_AUTO;
> > > + m->version = DEFAULT_CPU_VERSION;
> >
> > with this being the remaining user of macro just drop it and use 1 directly.
> >
> > > m->is_alias = true;
> > > x86_register_cpu_model_type(def->name, m);
> > >
> > > diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> > > index b26e25ba15..bdbe54b26f 100644
> > > --- a/target/i386/cpu.h
> > > +++ b/target/i386/cpu.h
> > > @@ -2679,27 +2679,14 @@ void cpu_report_tpr_access(CPUX86State *env,
> > > TPRAccess access);
> > > void apic_handle_tpr_access_report(DeviceState *d, target_ulong ip,
> > > TPRAccess access);
> > >
> > > -/* Special values for X86CPUVersion: */
> > > -
> > > -/* Resolve to latest CPU version */
> > > -#define CPU_VERSION_LATEST -1
> > > -
> > > -/*
> > > - * Resolve to version defined by current machine type.
> > > - * See x86_cpu_set_default_version()
> > > - */
> > > -#define CPU_VERSION_AUTO -2
> > > -
> > > -/* Don't resolve to any versioned CPU models, like old QEMU versions */
> > > -#define CPU_VERSION_LEGACY 0
> > > -
> > > typedef int X86CPUVersion;
> > >
> > > /*
> > > - * Set default CPU model version for CPU models having
> > > - * version == CPU_VERSION_AUTO.
> > > + * Set CPU model version to the lastest version.
> > > + * Currently, this is only used by microvm.
> > > */
> > > -void x86_cpu_set_default_version(X86CPUVersion version);
> > > +void x86_cpu_uses_lastest_version(void);
> > > +void x86_cpu_set_legacy_version(void);
> > >
> > > #ifndef CONFIG_USER_ONLY
> > >
> >
