Re: [PATCH v2 1/2] ppc/pnv.c: add a friendly warning when accel=kvm is used

[David Gibson]

On Tue, Nov 30, 2021 at 10:31:52AM -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>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

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

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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