Re: [PATCH v16 04/99] qtest/arm-cpu-features: Use generic qtest_has_accel() to check for KVM

[Claudio Fontana]

On 6/8/21 2:39 PM, Philippe Mathieu-Daudé wrote:
> On 6/8/21 12:49 PM, Philippe Mathieu-Daudé wrote:
>> On 6/8/21 10:22 AM, Philippe Mathieu-Daudé wrote:
>>> On 6/7/21 3:22 PM, Thomas Huth wrote:
>>>> On 04/06/2021 17.51, Alex Bennée wrote:
>>>>> From: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>>>
>>>>> Use the recently added generic qtest_has_accel() method to
>>>>> check if KVM is available.
>>>>>
>>>>> Suggested-by: Claudio Fontana <cfontana@suse.de>
>>>>> Reviewed-by: Andrew Jones <drjones@redhat.com>
>>>>> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
>>>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>>>>> Message-Id: <20210505125806.1263441-5-philmd@redhat.com>
>>>>> ---
>>>>>   tests/qtest/arm-cpu-features.c | 25 +------------------------
>>>>>   1 file changed, 1 insertion(+), 24 deletions(-)
>>>>>
>>>>> diff --git a/tests/qtest/arm-cpu-features.c
>>>>> b/tests/qtest/arm-cpu-features.c
>>>>> index 8252b85bb8..7f4b252127 100644
>>>>> --- a/tests/qtest/arm-cpu-features.c
>>>>> +++ b/tests/qtest/arm-cpu-features.c
>>>>> @@ -26,21 +26,6 @@
>>>>>                       "  'arguments': { 'type': 'full', "
>>>>>   #define QUERY_TAIL  "}}"
>>>>>   -static bool kvm_enabled(QTestState *qts)
>>>>> -{
>>>>> -    QDict *resp, *qdict;
>>>>> -    bool enabled;
>>>>> -
>>>>> -    resp = qtest_qmp(qts, "{ 'execute': 'query-kvm' }");
>>>>> -    g_assert(qdict_haskey(resp, "return"));
>>>>> -    qdict = qdict_get_qdict(resp, "return");
>>>>> -    g_assert(qdict_haskey(qdict, "enabled"));
>>>>> -    enabled = qdict_get_bool(qdict, "enabled");
>>>>> -    qobject_unref(resp);
>>>>> -
>>>>> -    return enabled;
>>>>> -}
>>>>> -
>>>>>   static QDict *do_query_no_props(QTestState *qts, const char *cpu_type)
>>>>>   {
>>>>>       return qtest_qmp(qts, QUERY_HEAD "'model': { 'name': %s }"
>>>>> @@ -493,14 +478,6 @@ static void
>>>>> test_query_cpu_model_expansion_kvm(const void *data)
>>>>>         qts = qtest_init(MACHINE_KVM "-cpu max");
>>>>>   -    /*
>>>>> -     * These tests target the 'host' CPU type, so KVM must be enabled.
>>>>> -     */
>>>>> -    if (!kvm_enabled(qts)) {
>>>>> -        qtest_quit(qts);
>>>>> -        return;
>>>>> -    }
>>>>> -
>>>>>       /* Enabling and disabling kvm-no-adjvtime should always work. */
>>>>>       assert_has_feature_disabled(qts, "host", "kvm-no-adjvtime");
>>>>>       assert_set_feature(qts, "host", "kvm-no-adjvtime", true);
>>>>> @@ -624,7 +601,7 @@ int main(int argc, char **argv)
>>>>>        * order avoid attempting to run an AArch32 QEMU with KVM on
>>>>>        * AArch64 hosts. That won't work and isn't easy to detect.
>>>>>        */
>>>>> -    if (g_str_equal(qtest_get_arch(), "aarch64")) {
>>>>> +    if (g_str_equal(qtest_get_arch(), "aarch64") &&
>>>>> qtest_has_accel("kvm")) {
>>>>>           qtest_add_data_func("/arm/kvm/query-cpu-model-expansion",
>>>>>                               NULL, test_query_cpu_model_expansion_kvm);
>>>>
>>>> I think this is wrong: query-kvm checks whether kvm is *enabled*, while
>>>> your new function only checks whether kvm has been built into the
>>>> binary. There is still the possibility that kvm has been built into the
>>>> binary, but is not available on the host, so in that case the test will
>>>> fail now.
>>
>> Not enough coffee earlier. I think this is a documentation problem,
>> query-kvm returns a list of *runtime* accelerators:
>> https://www.mail-archive.com/qemu-devel@nongnu.org/msg811144.html
>>
>> IIUC what Paolo said, if something asks for an accelerator that
>> is not present at build-time, then this is a configuration problem,
>> not relevant for the management interface.
> 
> Argh no... sigh. So we have 4 cases:
> 
> 1- accelerator not built
> 2- accelerator built in as module but not loaded
> 3- accelerator built in & loaded but not usable
> 4- accelerator built in & loaded and usable
> 
> QMP query-accels returns "accelerator built in & loaded"
> without precising it is usable.
> 
> qtest kvm_enabled() checks if the accelerator is enabled
> without checking it is built-in.
> 
> QMP query-kvm returns 'present' as in built-in (so case 1),
> and 'enabled' (a.k.a. 'allowed') updated once init_machine()
> succeeded (so case 4).
> 
> So, again, IIUC Paolo, what he said is for the management layer
> 1 and 2 are the same, the accelerator is not present.
> 
> For qtests, we want the 'usable' case (4) right? Whether the
> accelerator is builtin / loaded is irrelevant.
> 
> Could we improve the terminology here? Maybe is_present() and
> is_usable()? Suggestions?


Let me try some terms:

1 - bool accelerator_built()      ->   accelerator has been part of this QEMU 
build.
2 - bool accelerator_loaded()     ->   accelerator has been loaded, either 
because it is built-in, or because its code has been dynamically loaded

and probably the management layers do not care about the distinction between 1, 
2.

Maybe instead of "usable", "available" is better?

3 - bool accelerator_available()

Then we have the accelerator that is actually active, selected or chosen.

4 - bool accelerator_enabled()? bool accelerator_active()? bool 
accelerator_chosen()? bool accelerator_used()?

We already use the term "allowed", with different meaning and implementations 
depending on --enable-xxx,
which is quite confusing I think..


Ciao,

Claudoi


> 
> Do we need to add both query-present-accels query-usable-accels
> commands? Is it actually possible to return an array of 'usable'
> accelerators?
> 
> Maybe simply add query-present-accels() -> [] and
> query-usable-accel(accel) -> bool.
> 
>>
>>>>
>>>> Thus please drop / rework this patch.
>>>
>>> Indeed, this is unfortunate :(
>>>
>