Re: [Qemu-devel] Cubietruck: cannot create KVM guests: "kvm_init_vcpu failed: Invalid argument"

["Richard W.M. Jones" <rjones@redhat.com>]

On Tue, Dec 09, 2014 at 10:53:41AM +0000, Peter Maydell wrote:
> On 9 December 2014 at 10:50, Kashyap Chamarthy <kchamart@redhat.com> wrote:
> > Booting a minimal KVM guest throws the below error on Cubietruck:
> >
> >   "kvm_init_vcpu failed: Invalid argument"
> >
> > More context and an easy reproducer in this QEMU bug[1] for Fedora.
> >
> > Context quoting Rich Jones from comment #2:
> >
> >     "For some reason I thought this had been fixed upstream, but
> >     now that I've finally got my CT working again, I see that I
> >     am still carrying that patch in my custom qemu.
> >
> >     diff --git a/target-arm/cpu.c b/target-arm/cpu.c
> >     index 5ce7350..04d69d1 100644
> >     --- a/target-arm/cpu.c
> >     +++ b/target-arm/cpu.c
> >     @@ -858,7 +858,7 @@ static void cortex_a15_initfn(Object *obj)
> >          set_feature(&cpu->env, ARM_FEATURE_DUMMY_C15_REGS);
> >          set_feature(&cpu->env, ARM_FEATURE_CBAR_RO);
> >          set_feature(&cpu->env, ARM_FEATURE_LPAE);
> >     -    cpu->kvm_target = QEMU_KVM_ARM_TARGET_CORTEX_A15;
> >     +    cpu->kvm_target = QEMU_KVM_ARM_TARGET_CORTEX_A7;
> >          cpu->midr = 0x412fc0f1;
> >          cpu->reset_fpsid = 0x410430f0;
> >          cpu->mvfr0 = 0x10110222;
> 
> This is obviously a bogus patch -- this is the initfn
> for Cortex-A15 so telling it to be a Cortex-A7 is wrong
> (and would break working setups on A15 hosts).

Yes, I definitely was not proposing this as a serious patch!  In my
copy of qemu it has "HACK" in all capital letters in the summary ...

> >     So that's the answer really, it's a qemu bug.  Actually it looks as
> >     if qemu contains some code to try to get the host CPU type, but it
> >     doesn't work, or maybe we need to pass a -cpu option ..."
> 
> Yes, you need to pass a -cpu option. For KVM on ARM, you
> always need to either:
>  * pass a -cpu option matching the host CPU
>  * pass "-cpu host"
> 
> The CubieTruck is a Cortex-A7, which we don't have specific
> support for in QEMU, so you will need "-cpu host".

Kashyap ^^ can you try this?  Should be a trivial one-liner change
in src/launch-direct.c.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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