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Re: [PATCH v5] hw/i386/cpu: remove default_cpu_version and simplify
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From: |
Ani Sinha |
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Subject: |
Re: [PATCH v5] hw/i386/cpu: remove default_cpu_version and simplify |
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Date: |
Sat, 25 Jan 2025 08:58:16 +0530 |
On Thu, Jan 23, 2025 at 7:52 PM Igor Mammedov <imammedo@redhat.com> wrote:
>
> On Thu, 23 Jan 2025 17:26:12 +0530
> Ani Sinha <anisinha@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.
>
>
> Testing current master:
> ====
> ./qemu-system-x86_64 -M pc-i440fx-4.0 -cpu Haswell-v4 -monitor stdio
> ...
> (qemu) info hotpluggable-cpus
> Hotpluggable CPUs:
> type: "Haswell-v4-x86_64-cpu"
>
> we can run versioned on old machine types. with caveat
> not being able to migrate to old qemu that doesn't have it
>
> ====
> ./qemu-system-x86_64 -M pc-i440fx-4.0 -cpu Haswell -monitor stdio
> ...
> (qemu) info hotpluggable-cpus
> Hotpluggable CPUs:
> type: "Haswell-x86_64-cpu"
>
> ====
> ./qemu-system-x86_64 -M pc-i440fx-5.0 -cpu Haswell -monitor stdio
> ...
> (qemu) info hotpluggable-cpus
> Hotpluggable CPUs:
> type: "Haswell-x86_64-cpu"
>
> non-versioned model resolves to the same type regardless of legacy
>
> Do we really have to keep CPU_VERSION_LEGACY code around?
>
> Lets assume we drop all CPU_VERSION_LEGACY code, what would change?
>From code, x86_cpu_class_get_alias_of() always returns NULL for
legacy. Maybe somewhere the descriptions are different?
To be safe, I would just wait for another 10 months to drop all legacy stuff.
>
> > - 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 constant machine type. Therefore, for
> ^^^^^^^^^^^^^^^^^^
> s/.../versioned .../
>
> > 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: imammedo@redhat.com
> > Signed-off-by: Ani Sinha <anisinha@redhat.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
> >
> > 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();
> > + 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)
> > +{
> > + 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);
> > +
> > + 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;
> > +}
> >
> > -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;
> > +
> > + 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);
> > - }
> > }
> > 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;
> > }
> >
> > @@ -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;
> > }
> >
> > @@ -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;
> > 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
> >
>