Re: [Qemu-devel] Could not boot a guest vm from kvm mode based on APM X-Gene Host and latest qemu

[Peter Maydell]

On 15 September 2015 at 01:03, liang yan <address@hidden> wrote:
> Hello, All,
>
> I am trying to enable kvm for a guest vm on an APM X-Gene Host with latest
> qemu, but could not make it work.
>
> The host is APM X-Gene 8-core, Linux kernel is 4.1.0-rc7-1-arm64,
>
> Guest kernel is linux-3.16rc3
>
> QEMU is latest version
>
> Host has these dmesg info
> [    2.708259] kvm [1]: GICH base=0x780c0000, GICV base=0x780e0000, IRQ=25
> [    2.708327] kvm [1]: timer IRQ30
> [    2.708335] kvm [1]: Hyp mode initialized successfully
>
> Host has dev/kvm.
>
> command-line is
> aarch64-softmmu/qemu-system-aarch64 -machine virt,kernel_irqchip=off -cpu
> cortex-a57 -machine accel=kvm -nographic -smp 1 -m 2048 -kernel
> aarch64-linux-3.16rc3-buildroot.img  --append "console=ttyAMA0"
>
>
> when using cpu "cortex-a57", got the error "kvm_init_vcpu failed: Invalid
> argument"
> when using cpu "host", got the error "Failed to retrieve host CPU features!"

-cpu host is the correct option here (as Tushar says, specifying
a CPU other than the one your host has won't work until the
functionality he's working on is done).

The error message you get when you try '-cpu host' indicates that
kvm_arm_get_host_cpu_features() failed. That function
really just does a "create scratch VM", so it is exercising the
basic kernel "create VM" operations. It (and the function
kvm_arm_create_scratch_host_vcpu() that it calls) are fairly
short and simple, so I would suggest either singlestepping
through them with a debugger or adding diagnostic printfs
to find out which system call is failing.

My gut feeling is that this is a bug or missing feature in your
host kernel.

thanks
-- PMM