Re: [PATCH v2 01/11] accel/kvm: Check MachineClass kvm_type() return value

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 2/22/21 6:50 PM, Cornelia Huck wrote:
> On Mon, 22 Feb 2021 18:41:07 +0100
> Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
> 
>> On 2/22/21 6:24 PM, Cornelia Huck wrote:
>>> On Fri, 19 Feb 2021 18:38:37 +0100
>>> Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
>>>   
>>>> MachineClass::kvm_type() can return -1 on failure.
>>>> Document it, and add a check in kvm_init().
>>>>
>>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>> ---
>>>>  include/hw/boards.h | 3 ++-
>>>>  accel/kvm/kvm-all.c | 6 ++++++
>>>>  2 files changed, 8 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/include/hw/boards.h b/include/hw/boards.h
>>>> index a46dfe5d1a6..68d3d10f6b0 100644
>>>> --- a/include/hw/boards.h
>>>> +++ b/include/hw/boards.h
>>>> @@ -127,7 +127,8 @@ typedef struct {
>>>>   *    implement and a stub device is required.
>>>>   * @kvm_type:
>>>>   *    Return the type of KVM corresponding to the kvm-type string option or
>>>> - *    computed based on other criteria such as the host kernel capabilities.
>>>> + *    computed based on other criteria such as the host kernel capabilities
>>>> + *    (which can't be negative), or -1 on error.
>>>>   * @numa_mem_supported:
>>>>   *    true if '--numa node.mem' option is supported and false otherwise
>>>>   * @smp_parse:
>>>> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
>>>> index 84c943fcdb2..b069938d881 100644
>>>> --- a/accel/kvm/kvm-all.c
>>>> +++ b/accel/kvm/kvm-all.c
>>>> @@ -2057,6 +2057,12 @@ static int kvm_init(MachineState *ms)
>>>>                                                              "kvm-type",
>>>>                                                              &error_abort);
>>>>          type = mc->kvm_type(ms, kvm_type);
>>>> +        if (type < 0) {
>>>> +            ret = -EINVAL;
>>>> +            fprintf(stderr, "Failed to detect kvm-type for machine '%s'\n",
>>>> +                    mc->name);
>>>> +            goto err;
>>>> +        }
>>>>      }
>>>>  
>>>>      do {  
>>>
>>> No objection to this patch; but I'm wondering why some non-pseries
>>> machines implement the kvm_type callback, when I see the kvm-type
>>> property only for pseries? Am I holding my git grep wrong?  
>>
>> Can it be what David commented here?
>> https://www.mail-archive.com/qemu-devel@nongnu.org/msg784508.html
>>
> 
> Ok, I might be confused about the other ppc machines; but I'm wondering
> about the kvm_type callback for mips and arm/virt. Maybe I'm just
> confused by the whole mechanism?

For MIPS see https://www.linux-kvm.org/images/f/f2/01x08a-MIPS.pdf
and Jiaxun comment here:
https://lore.kernel.org/linux-mips/a2a2cfe3-5618-43b1-a6a4-cc768fc1b9fb@www.fastmail.com/

TE KVM: Trap-and-Emul guest kernel
VZ KVM: HW Virtualized

For "the whole mechanism" I'll defer to Paolo =)