Re: [PATCH v2 08/16] target/riscv: move 'vlen' to riscv_cpu_properties[]

[Daniel Henrique Barboza]

On 12/29/23 08:22, Vladimir Isaev wrote:
> 22.12.2023 15:22, Daniel Henrique Barboza wrote:
> > Turning 'vlen' into a class property will allow its default value to be
> > overwritten by cpu_init() later on, solving the issue we have now where
> > CPU specific settings are getting overwritten by the default.
> >
> > For 'vlen', 'elen' and the blocksize options we need a way of tracking
> > if the user set a value for them. This is benign for TCG since the cost
> > of always validating these values are small, but for KVM we need syscalls
> > to read the host values to make the validations. Knowing whether the
> > user didn't touch the values makes a difference. We'll track user setting
> > for these properties using a hash, like we do in the TCG driver.
> >
> > Common validation bits are moved from riscv_cpu_validate_v() to
> > prop_vlen_set() to be shared with KVM.
> >
> > And, as done with every option we migrated to riscv_cpu_properties[],
> > vendor CPUs can't have their 'vlen' value changed.
> >
> > Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> > ---
> >   target/riscv/cpu.c         | 63 +++++++++++++++++++++++++++++++++++++-
> >   target/riscv/tcg/tcg-cpu.c |  5 ---
> >   2 files changed, 62 insertions(+), 6 deletions(-)
> >
> > diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> > index d6625399a7..c2ff50bcab 100644
> > --- a/target/riscv/cpu.c
> > +++ b/target/riscv/cpu.c
> > @@ -29,6 +29,7 @@
> >   #include "qapi/visitor.h"
> >   #include "qemu/error-report.h"
> >   #include "hw/qdev-properties.h"
> > +#include "hw/core/qdev-prop-internal.h"
> >   #include "migration/vmstate.h"
> >   #include "fpu/softfloat-helpers.h"
> >   #include "sysemu/kvm.h"
> > @@ -53,6 +54,15 @@ const uint32_t misa_bits[] = {RVI, RVE, RVM, RVA, RVF, RVD, 
> > RVV,
> >   #define BYTE(x)   (x)
> >   #endif
> >
> > +/* Hash that stores general user set numeric options */
> > +static GHashTable *general_user_opts;
> > +
> > +static void cpu_option_add_user_setting(const char *optname, uint32_t value)
> > +{
> > +    g_hash_table_insert(general_user_opts, (gpointer)optname,
> > +                        GUINT_TO_POINTER(value));
> > +}
> > +
> >   #define ISA_EXT_DATA_ENTRY(_name, _min_ver, _prop) \
> >       {#_name, _min_ver, CPU_CFG_OFFSET(_prop)}
> >
> > @@ -1244,6 +1254,8 @@ static void riscv_cpu_init(Object *obj)
> >                         IRQ_LOCAL_MAX + IRQ_LOCAL_GUEST_MAX);
> >   #endif /* CONFIG_USER_ONLY */
> >
> > +    general_user_opts = g_hash_table_new(g_str_hash, g_str_equal);
> > +
> >       /*
> >        * The timer and performance counters extensions were supported
> >        * in QEMU before they were added as discrete extensions in the
> > @@ -1664,8 +1676,54 @@ static const PropertyInfo prop_vext_spec = {
> >       .set = prop_vext_spec_set,
> >   };
> >
> > +static void prop_vlen_set(Object *obj, Visitor *v, const char *name,
> > +                         void *opaque, Error **errp)
> > +{
> > +    RISCVCPU *cpu = RISCV_CPU(obj);
> > +    uint16_t value;
> > +
> > +    if (!visit_type_uint16(v, name, &value, errp)) {
> > +        return;
> > +    }
> > +
> > +    if (!is_power_of_2(value)) {
> > +        error_setg(errp, "Vector extension VLEN must be power of 2");
> > +        return;
> > +    }
> > +
> > +    /* Always allow setting a default value */
>
> What is the case for vlen equal to 0? Since in properties it is defined with 
> default value set to 128.

The process of setting a default uses the default setter of the property. I.e.
when setting vlen default value to 128, this function will be called with
value = 128 when cpu->cfg.vlen is 0.

If we don't special case this scenario we'll fail the "vendor CPUs don't allow
changing vlen" check that comes right after.


Thanks,

Daniel

> > +    if (cpu->cfg.vlen == 0) {
> > +        cpu->cfg.vlen = value;
> > +        return;
> > +    }
> > +
> > +    if (value != cpu->cfg.vlen && riscv_cpu_is_vendor(obj)) {
> > +        cpu_set_prop_err(cpu, name, errp);
> > +        error_append_hint(errp, "Current '%s' val: %u\n",
> > +                          name, cpu->cfg.vlen);
> > +        return;
> > +    }
> > +
> > +    cpu_option_add_user_setting(name, value);
> > +    cpu->cfg.vlen = value;
> > +}
> > +
> > +static void prop_vlen_get(Object *obj, Visitor *v, const char *name,
> > +                         void *opaque, Error **errp)
> > +{
> > +    uint16_t value = RISCV_CPU(obj)->cfg.vlen;
> > +
> > +    visit_type_uint16(v, name, &value, errp);
> > +}
> > +
> > +static const PropertyInfo prop_vlen = {
> > +    .name = "vlen",
> > +    .get = prop_vlen_get,
> > +    .set = prop_vlen_set,
> > +    .set_default_value = qdev_propinfo_set_default_value_uint,
> > +};
> > +
> >   Property riscv_cpu_options[] = {
> > -    DEFINE_PROP_UINT16("vlen", RISCVCPU, cfg.vlen, 128),
> >       DEFINE_PROP_UINT16("elen", RISCVCPU, cfg.elen, 64),
> >
> >       DEFINE_PROP_UINT16("cbom_blocksize", RISCVCPU, cfg.cbom_blocksize, 64),
> > @@ -1687,6 +1745,9 @@ static Property riscv_cpu_properties[] = {
> >       {.name = "priv_spec", .info = &prop_priv_spec},
> >       {.name = "vext_spec", .info = &prop_vext_spec},
> >
> > +    {.name = "vlen", .info = &prop_vlen,
> > +     .set_default = true, .defval.u = 128},
> > +
> >   #ifndef CONFIG_USER_ONLY
> >       DEFINE_PROP_UINT64("resetvec", RISCVCPU, env.resetvec, DEFAULT_RSTVEC),
> >   #endif
> > diff --git a/target/riscv/tcg/tcg-cpu.c b/target/riscv/tcg/tcg-cpu.c
> > index 6501c29d8e..8ec858e096 100644
> > --- a/target/riscv/tcg/tcg-cpu.c
> > +++ b/target/riscv/tcg/tcg-cpu.c
> > @@ -178,11 +178,6 @@ static void riscv_cpu_validate_misa_mxl(RISCVCPU *cpu, 
> > Error **errp)
> >   static void riscv_cpu_validate_v(CPURISCVState *env, RISCVCPUConfig *cfg,
> >                                    Error **errp)
> >   {
> > -    if (!is_power_of_2(cfg->vlen)) {
> > -        error_setg(errp, "Vector extension VLEN must be power of 2");
> > -        return;
> > -    }
> > -
> >       if (cfg->vlen > RV_VLEN_MAX || cfg->vlen < 128) {
> >           error_setg(errp,
> >                      "Vector extension implementation only supports VLEN "
> > --
> > 2.43.0