Re: [PATCH 1/1] ppc/pnv.c: add a friendly warning when accel=kvm is used

["Cédric Le Goater" <clg@kaod.org>]

On 11/26/21 02:11, David Gibson wrote:
> On Thu, Nov 25, 2021 at 07:42:02PM -0300, Daniel Henrique Barboza wrote:
>> If one tries to use -machine powernv9,accel=kvm in a Power9 host, a
>> cryptic error will be shown:
>>
>> qemu-system-ppc64: Register sync failed... If you're using kvm-hv.ko, only "-cpu host" is possible
>> qemu-system-ppc64: kvm_init_vcpu: kvm_arch_init_vcpu failed (0): Invalid argument
>>
>> Appending '-cpu host' will throw another error:
>>
>> qemu-system-ppc64: invalid chip model 'host' for powernv9 machine
>>
>> The root cause is that in IBM PowerPC we have different specs for the bare-metal
>> and the guests. The bare-metal follows OPAL, the guests follow PAPR. The kernel
>> KVM modules presented in the ppc kernels implements PAPR. This means that we
>> can't use KVM accel when using the powernv machine, which is the emulation of
>> the bare-metal host.
>>
>> All that said, let's give a more informative error in this case.
>>
>> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
>> ---
>>   hw/ppc/pnv.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/hw/ppc/pnv.c b/hw/ppc/pnv.c
>> index 71e45515f1..e5b87e8730 100644
>> --- a/hw/ppc/pnv.c
>> +++ b/hw/ppc/pnv.c
>> @@ -742,6 +742,11 @@ static void pnv_init(MachineState *machine)
>>       DriveInfo *pnor = drive_get(IF_MTD, 0, 0);
>>       DeviceState *dev;
>>   
>> +    if (kvm_enabled()) {
>> +        error_report("The powernv machine does not work with KVM acceleration");
>> +        exit(EXIT_FAILURE);
>> +    }
> 
> 
> Hmm.. my only concern here is that powernv could, at least
> theoretically, work with KVM PR.  I don't think it does right now,
> though.

At the same time, it is nice to not let the user think that it could work
in its current state. Don't you think so ?

C.

> 
>> +
>>       /* allocate RAM */
>>       if (machine->ram_size < mc->default_ram_size) {
>>           char *sz = size_to_str(mc->default_ram_size);
>