Re: [PATCH v2 09/21] hw/vfio/pci: Convert CONFIG_KVM check to runtime one

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 10/3/25 13:54, BALATON Zoltan wrote:
> On Mon, 10 Mar 2025, Eric Auger wrote:
>> Hi Philippe,
>>
>> On 3/9/25 12:09 AM, Philippe Mathieu-Daudé wrote:
>>> Use the runtime kvm_enabled() helper to check whether
>>> KVM is available or not.
>>
>> Miss the "why" of this patch.
>>
>> By the way I fail to remember/see where kvm_allowed is set.

In accel/accel-system.c:

     int accel_init_machine(AccelState *accel, MachineState *ms)
     {
         AccelClass *acc = ACCEL_GET_CLASS(accel);
         int ret;
         ms->accelerator = accel;
         *(acc->allowed) = true;
         ret = acc->init_machine(ms);
         if (ret < 0) {
             ms->accelerator = NULL;
             *(acc->allowed) = false;
             object_unref(OBJECT(accel));
         } else {
             object_set_accelerator_compat_props(acc->compat_props);
         }
         return ret;
     }

> 
> It's in include/system/kvm.h
> 
>> I am also confused because we still have some code, like in
>> vfio/common.c which does both checks:
>> #ifdef CONFIG_KVM
>>         if (kvm_enabled()) {
>>             max_memslots = kvm_get_max_memslots();
>>         }
>> #endif

We should prefer kvm_enabled() over CONFIG_KVM, but for kvm_enabled()
we need the prototypes declared, which sometimes aren't.