Re: [PATCH 3/4] target/riscv/kvm: add kvm-aia bools props

[Daniel Henrique Barboza <dbarboza@ventanamicro.com>]

On 10/10/24 10:57 PM, Alistair Francis wrote:
> On Tue, Sep 24, 2024 at 10:46 PM Daniel Henrique Barboza
> <dbarboza@ventanamicro.com> wrote:
>>
>> Boolean properties are preferrable in comparision to string properties
>> since they don't require a string parsing.
>>
>> Add three bools that represents the available kvm-aia mode:
>> riscv-aia-emul, riscv-aia-hwaccel, riscv-aia-auto. They work like the
>> existing riscv-aia string property, i.e. if no bool is set we'll default
>> to riscv-aia-auto, if the host supports it.
>>
>> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
>> ---
>>   target/riscv/kvm/kvm-cpu.c | 77 ++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 77 insertions(+)
>>
>> diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
>> index 32f3dd6a43..e256e3fc48 100644
>> --- a/target/riscv/kvm/kvm-cpu.c
>> +++ b/target/riscv/kvm/kvm-cpu.c
>> @@ -1671,6 +1671,62 @@ static void riscv_set_kvm_aia(Object *obj, const char *val, Error **errp)
>>       }
>>   }
>>
>> +static void riscv_set_kvm_aia_bool(uint32_t aia_bool, bool val)
>> +{
>> +    bool default_aia_mode = KVM_DEV_RISCV_AIA_MODE_AUTO;
>> +
>> +    g_assert(aia_bool <= KVM_DEV_RISCV_AIA_MODE_AUTO);
>> +
>> +    if (val) {
>> +        aia_mode = aia_bool;
>> +        return;
>> +    }
>> +
>> +    /*
>> +     * Setting an aia_bool to 'false' does nothing if
>> +     * aia_mode isn't set to aia_bool.
>> +     */
>> +    if (aia_mode != aia_bool) {
>> +        return;
>> +    }
>> +
>> +    /*
>> +     * Return to default value if we're disabling the
>> +     * current set aia_mode.
>> +     */
>> +    aia_mode = default_aia_mode;
>> +}
>> +
>> +static bool riscv_get_kvm_aia_emul(Object *obj, Error **errp)
>> +{
>> +    return aia_mode == KVM_DEV_RISCV_AIA_MODE_EMUL;
>> +}
>> +
>> +static void riscv_set_kvm_aia_emul(Object *obj,  bool val, Error **errp)
>> +{
>> +    riscv_set_kvm_aia_bool(KVM_DEV_RISCV_AIA_MODE_EMUL, val);
>> +}
>> +
>> +static bool riscv_get_kvm_aia_hwaccel(Object *obj, Error **errp)
>> +{
>> +    return aia_mode == KVM_DEV_RISCV_AIA_MODE_HWACCEL;
>> +}
>> +
>> +static void riscv_set_kvm_aia_hwaccel(Object *obj,  bool val, Error **errp)
>> +{
>> +    riscv_set_kvm_aia_bool(KVM_DEV_RISCV_AIA_MODE_HWACCEL, val);
>> +}
>> +
>> +static bool riscv_get_kvm_aia_auto(Object *obj, Error **errp)
>> +{
>> +    return aia_mode == KVM_DEV_RISCV_AIA_MODE_AUTO;
>> +}
>> +
>> +static void riscv_set_kvm_aia_auto(Object *obj,  bool val, Error **errp)
>> +{
>> +    riscv_set_kvm_aia_bool(KVM_DEV_RISCV_AIA_MODE_AUTO, val);
>> +}
>> +
>>   void kvm_arch_accel_class_init(ObjectClass *oc)
>>   {
>>       object_class_property_add_str(oc, "riscv-aia", riscv_get_kvm_aia,
>> @@ -1681,6 +1737,27 @@ void kvm_arch_accel_class_init(ObjectClass *oc)
>>           "if the host supports it");
>>       object_property_set_default_str(object_class_property_find(oc, "riscv-aia"),
>>                                       "auto");
>> +
>> +    object_class_property_add_bool(oc, "riscv-aia-emul",
>> +                                   riscv_get_kvm_aia_emul,
>> +                                   riscv_set_kvm_aia_emul);
>> +    object_class_property_set_description(oc, "riscv-aia-emul",
>> +        "Set KVM AIA mode to 'emul'. Changing KVM AIA modes relies on host "
>> +        "support. Default mode is 'auto' if the host supports it");
>> +
>> +    object_class_property_add_bool(oc, "riscv-aia-hwaccel",
>> +                                   riscv_get_kvm_aia_hwaccel,
>> +                                   riscv_set_kvm_aia_hwaccel);
>> +    object_class_property_set_description(oc, "riscv-aia-hwaccel",
>> +        "Set KVM AIA mode to 'hwaccel'. Changing KVM AIA modes relies on host "
>> +        "support. Default mode is 'auto' if the host supports it");
>> +
>> +    object_class_property_add_bool(oc, "riscv-aia-auto",
>> +                                   riscv_get_kvm_aia_auto,
>> +                                   riscv_set_kvm_aia_auto);
>> +    object_class_property_set_description(oc, "riscv-aia-auto",
>> +        "Set KVM AIA mode to 'auto'. Changing KVM AIA modes "
>> +        "relies on host support");
> 
> This seems more confusing. What should happen if a user sets multiple to true?

It'll work like most options in QEMU: the last setting will overwrite the previous
ones. "-accel kvm,riscv-aia-hwaccel=true,riscv-aia-emul=true" will set the mode
to 'emul'. This is the same behavior that we have with the existing 'riscv-aia'
string option.

In case someone tries it out with multiple -accel options, this doesn't work. Only
the first '-accel <type>' are parsed. This happens due to a known command line
parsing/accel globals issue that I tried to fix in [1] and [2].

For now, using the existing 'riscv-aia' string option:

-accel kvm,riscv-aia=emul -accel kvm,riscv-aia=hwaccel -accel kvm,riscv-aia=auto

This will set riscv-aia to "emul" because all other "-accel kvm" options aren't
being parsed. You can do silly stuff like:

-accel kvm,riscv-aia=emul -accel kvm,riscv-aia=this_is_not_an_option

And the guest will boot normally, setting riscv-aia to 'emul'.


Thanks,

Daniel


[1] "[PATCH 0/2] system/vl.c: parse all '-accel' opts"
     https://lore.kernel.org/qemu-devel/20240701133038.1489043-1-dbarboza@ventanamicro.com/
[2] "[PATCH v2 0/2] object,accel-system: allow Accel type globals"
     https://lore.kernel.org/qemu-devel/20240703204149.1957136-1-dbarboza@ventanamicro.com/


> 
> Alistair
> 
>>   }
>>
>>   void kvm_riscv_aia_create(MachineState *machine, uint64_t group_shift,
>> --
>> 2.45.2
>>
>>