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Re: [PATCH v2] hw/i386/cpu: remove default_cpu_version and simplify
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From: |
Ani Sinha |
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Subject: |
Re: [PATCH v2] hw/i386/cpu: remove default_cpu_version and simplify |
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Date: |
Thu, 16 Jan 2025 08:44:57 +0530 |
On Wed, Jan 15, 2025 at 9:38 PM Ani Sinha <anisinha@redhat.com> wrote:
>
> On Wed, Jan 15, 2025 at 7:08 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Wed, Jan 15, 2025 at 11:33:10AM +0530, Ani Sinha wrote:
> > > On Thu, Dec 12, 2024 at 8:19 PM 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.
> > > > - 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
> > > > 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>
> > >
> > > Has this been picked up by anyone?
> >
> >
> > Fails CI:
> >
> > https://gitlab.com/mstredhat/qemu/-/jobs/8857478218
>
> Ah, very interesting! Subtle issue with the patch which is easily fixed
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 930ffd91b4..a4c64a4e1b 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -6287,7 +6287,7 @@ static void x86_cpu_apply_version_props(X86CPU
> *cpu, X86CPUModel *model)
> const X86CPUVersionDefinition *vdef;
> X86CPUVersion version = x86_cpu_model_resolve_version(model);
> - if (use_legacy_cpu) {
> + if (version == DEFAULT_CPU_VERSION && use_legacy_cpu) {
> return;
> }
> @@ -6317,7 +6317,7 @@ 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 (use_legacy_cpu) {
> + if (version == DEFAULT_CPU_VERSION && use_legacy_cpu) {
> return cache_info;
> }
>
> functional test that was failing seems to pass:
>
> $ pyvenv/bin/python3 ../tests/functional/test_x86_cpu_model_versions.py
>
> TAP version 13
> ok 1 test_x86_cpu_model_versions.CascadelakeArchCapabilities.test_4_0
> ok 2 test_x86_cpu_model_versions.CascadelakeArchCapabilities.test_4_1
> ok 3 test_x86_cpu_model_versions.CascadelakeArchCapabilities.test_set_4_0
> ok 4 test_x86_cpu_model_versions.CascadelakeArchCapabilities.test_unset_4_1
> ok 5 test_x86_cpu_model_versions.CascadelakeArchCapabilities.test_v1_4_0
> ok 6 test_x86_cpu_model_versions.CascadelakeArchCapabilities.test_v1_set_4_0
> ok 7 test_x86_cpu_model_versions.CascadelakeArchCapabilities.test_v2_4_0
> ok 8 test_x86_cpu_model_versions.CascadelakeArchCapabilities.test_v2_unset_4_1
> ok 9
> test_x86_cpu_model_versions.X86CPUModelAliases.test_4_0_alias_compatibility
> ok 10 test_x86_cpu_model_versions.X86CPUModelAliases.test_4_1_alias
> ok 11 test_x86_cpu_model_versions.X86CPUModelAliases.test_none_alias
> 1..11
>
> Will run some more tests and repost. Thanks!
pipeline has also passed https://gitlab.com/anisinha/qemu/-/pipelines/1626783632
>
> >
> > > > ---
> > > > hw/i386/microvm.c | 2 +-
> > > > hw/i386/pc_piix.c | 6 +++---
> > > > hw/i386/pc_q35.c | 6 +++---
> > > > hw/i386/x86-common.c | 15 ++++++++++---
> > > > include/hw/i386/pc.h | 21 +++++++++++++++---
> > > > include/hw/i386/x86.h | 5 ++++-
> > > > target/i386/cpu.c | 50 +++++++++++++++++++++----------------------
> > > > target/i386/cpu.h | 21 ++++--------------
> > > > 8 files changed, 69 insertions(+), 57 deletions(-)
> > > >
> > > > changelog:
> > > > v2: explain in commit log why use of CPU_VERSION_LATEST for machines
> > > > is problematic.
> > > >
> > > > diff --git a/hw/i386/microvm.c b/hw/i386/microvm.c
> > > > index 86637afa0f..2cbe08caea 100644
> > > > --- a/hw/i386/microvm.c
> > > > +++ b/hw/i386/microvm.c
> > > > @@ -458,7 +458,7 @@ static void microvm_machine_state_init(MachineState
> > > > *machine)
> > > >
> > > > microvm_memory_init(mms);
> > > >
> > > > - x86_cpus_init(x86ms, CPU_VERSION_LATEST);
> > > > + x86_cpus_init_with_latest_cpu_version(x86ms);
> > > >
> > > > microvm_devices_init(mms);
> > > > }
> > > > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> > > > index 2bf6865d40..8e0ab0387f 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);
> > > > @@ -454,7 +455,6 @@ 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)";
> > > > @@ -661,7 +661,7 @@ 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 8319b6d45e..9a4f14b336 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);
> > > > @@ -336,7 +337,6 @@ 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)";
> > > > @@ -537,7 +537,7 @@ 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 dc031af662..37dfdb7300 100644
> > > > --- a/hw/i386/x86-common.c
> > > > +++ b/hw/i386/x86-common.c
> > > > @@ -66,15 +66,24 @@ out:
> > > > object_unref(cpu);
> > > > }
> > > >
> > > > -void x86_cpus_init(X86MachineState *x86ms, int default_cpu_version)
> > > > +void x86_legacy_cpus_init(X86MachineState *x86ms)
> > > > +{
> > > > + machine_uses_legacy_cpu();
> > > > + x86_cpus_init(x86ms);
> > > > +}
> > > > +
> > > > +void x86_cpus_init_with_latest_cpu_version(X86MachineState *x86ms)
> > > > +{
> > > > + x86_cpu_uses_lastest_version();
> > > > + x86_cpus_init(x86ms);
> > > > +}
> > > > +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 14ee06287d..b514b957d9 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;
> > > > @@ -125,11 +122,29 @@ 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"
> > > > OBJECT_DECLARE_TYPE(PCMachineState, PCMachineClass, PC_MACHINE)
> > > >
> > > > +static inline 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_legacy_cpus_init(x86ms);
> > > > + } else {
> > > > + /* use non-legacy cpus */
> > > > + x86_cpus_init(x86ms);
> > > > + }
> > > > +}
> > > > +
> > > > /* ioapic.c */
> > > >
> > > > GSIState *pc_gsi_create(qemu_irq **irqs, bool pci_enabled);
> > > > diff --git a/include/hw/i386/x86.h b/include/hw/i386/x86.h
> > > > index d43cb3908e..a90464f74b 100644
> > > > --- a/include/hw/i386/x86.h
> > > > +++ b/include/hw/i386/x86.h
> > > > @@ -114,7 +114,10 @@ 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_legacy_cpus_init(X86MachineState *x86ms);
> > > > +void x86_cpus_init_with_latest_cpu_version(X86MachineState *x86ms);
> > > > +
> > > > 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 3725dbbc4b..14f5aa359b 100644
> > > > --- a/target/i386/cpu.c
> > > > +++ b/target/i386/cpu.c
> > > > @@ -191,6 +191,9 @@ 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 machine_uses_legacy_cpu(void)
> > > > +{
> > > > + use_legacy_cpu = true;
> > > > +}
> > > >
> > > > -void x86_cpu_set_default_version(X86CPUVersion version)
> > > > +static bool use_last_cpu_version;
> > > > +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_last_cpu_version = 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_last_cpu_version) {
> > > > return x86_cpu_model_last_version(model);
> > > > }
> > > > - return v;
> > > > +
> > > > + return model->version;
> > > > }
> > > >
> > > > static Property max_x86_cpu_properties[] = {
> > > > @@ -5986,6 +5982,12 @@ static char
> > > > *x86_cpu_class_get_alias_of(X86CPUClass *cc)
> > > > if (!cc->model || !cc->model->is_alias) {
> > > > return NULL;
> > > > }
> > > > +
> > > > + if (use_legacy_cpu) {
> > > > + /* legacy cpu models do not support cpu aliases */
> > > > + return NULL;
> > > > + }
> > > > +
> > > > version = x86_cpu_model_resolve_version(cc->model);
> > > > if (version <= 0) {
> > > > return NULL;
> > > > @@ -6003,11 +6005,7 @@ 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);
> > > > @@ -6114,7 +6112,7 @@ static void x86_cpu_definition_entry(gpointer
> > > > data, gpointer user_data)
> > > > * 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) {
> > > > + if (!use_legacy_cpu) {
> > > > info->alias_of = x86_cpu_class_get_alias_of(cc);
> > > > }
> > > >
> > > > @@ -6288,7 +6286,7 @@ 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 (use_legacy_cpu) {
> > > > return;
> > > > }
> > > >
> > > > @@ -6318,7 +6316,7 @@ 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 (use_legacy_cpu) {
> > > > return cache_info;
> > > > }
> > > >
> > > > @@ -6453,7 +6451,7 @@ 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 4c239a6970..5ad80c8a97 100644
> > > > --- a/target/i386/cpu.h
> > > > +++ b/target/i386/cpu.h
> > > > @@ -2658,28 +2658,15 @@ 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 machine_uses_legacy_cpu(void);
> > > > #ifndef CONFIG_USER_ONLY
> > > >
> > > > void do_cpu_sipi(X86CPU *cpu);
> > > > --
> > > > 2.45.2
> > > >
> >