Re: [Qemu-devel] [PATCH 2/4] mips_malta: Change default KVM cpu to 24Kc (no FP)

[Aurelien Jarno]

On Thu, Jun 26, 2014 at 10:44:23AM +0100, James Hogan wrote:
> Change the default Malta CPU model for when KVM is enabled to 24Kc which
> doesn't have floating point support compared to the 24Kf.
> 
> The resulting incorrect Config CP0 register value doesn't get passed to
> KVM yet as KVM doesn't expose it, however we should ensure it is set
> correctly now to reduce the risk of breaking migration/loadvm to a
> future version of QEMU/Linux that does support them.
> 
> Signed-off-by: James Hogan <address@hidden>
> Cc: Aurelien Jarno <address@hidden>
> Cc: Paolo Bonzini <address@hidden>
> ---
>  hw/mips/mips_malta.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/mips/mips_malta.c b/hw/mips/mips_malta.c
> index 2868ee5b0307..c0841991f4e9 100644
> --- a/hw/mips/mips_malta.c
> +++ b/hw/mips/mips_malta.c
> @@ -949,7 +949,12 @@ void mips_malta_init(MachineState *machine)
>  #ifdef TARGET_MIPS64
>          cpu_model = "20Kc";
>  #else
> -        cpu_model = "24Kf";
> +        if (kvm_enabled()) {
> +            /* Don't enable FPU on KVM yet */
> +            cpu_model = "24Kc";
> +        } else {
> +            cpu_model = "24Kf";
> +        }
>  #endif
>      }

Given the explanations in the other mails, that looks fine to me, that
said I think we should at least warn the user that we are disabling some
features, instead of doing it silently. This is what is done for example
on x86 when a CPU feature is not available.

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
address@hidden                 http://www.aurel32.net