[Qemu-devel] [Query] Does Linux & Qemu support KVM for ARM32 guest on ARM64 host

[Qemu-devel] [Query] Does Linux & Qemu support KVM for ARM32 guest on ARM64 host

[RAVINDRA KUMAR SANDE]

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Re: [Qemu-devel] [Query] Does Linux & Qemu support KVM for ARM32 guest on ARM64 host

[Shannon Zhao]

On 2016/4/28 9:50, RAVINDRA KUMAR SANDE wrote:
> 
> What I did  :
> 1) Just for investigation, I took a ARMv8 ( OdroidC2 ) board
> 2)  I compiled Linux 3.14 with KVM support for this ARMv8 ( OdroidC2 )
> board, with modification replacing meson_timer by arm timer in its dts
> file.
> Why Linux 3.14 : I took Linux 3.14 because display drivers for this
> board are officially for this version; and I am interested in seeing
> some Linux guest booting with display on.
> 3)  I see from boot log of  that KVM is initialized successfully, and I
> can see /dev/kvm node.
> 4) I built latest Qemu with --enable-kvm on this board natively.
> 
> What I find :
> 1) running "qemu-system-arm  -enable-kvm   -machine vexpress-a9 ...."
> gives error :  no accelerator found
> 2) running "qemu-system-aarch64 -enable-kvm  -machine vexpress-a9 ...."
> gives error : kmv_init_vcpu (IOCtl on /dev/kvm) failed, guest not supported
> ( I experimented some modifications as well to overcome above error,
> such as replacing value assigned to cpu->kvm_target etc, but IOCtl call
> is failing)
> 
> Query:
> 1) Does Arm64 Linux not enable KVM support for Arm32 guest ?
> 2) Can qemu-system-arm not use the KVM feature on Arm64 host ?
> 3) Can qemu-system-aarch64 not use KVM feature for Arm32 guest ?
> 
You can use below command to boot a ARM32 guest on ARM64：

qemu-system-aarch64 -enable-kvm -machine virt,kernel_irqchip=on -cpu
host,aarch64=off ....

-- 
Shannon

Re: [Qemu-devel] [Query] Does Linux & Qemu support KVM for ARM32 guest on ARM64 host

[RAVINDRA KUMAR SANDE]

> On 2016/4/28 9:50, RAVINDRA KUMAR SANDE wrote:
> > 
> > What I did  :
> > 1) Just for investigation, I took a ARMv8 ( OdroidC2 ) board
> > 2)  I compiled Linux 3.14 with KVM support for this ARMv8 ( OdroidC2 )
> > board, with modification replacing meson_timer by arm timer in its dts
> > file.
> > Why Linux 3.14 : I took Linux 3.14 because display drivers for this
> > board are officially for this version; and I am interested in seeing
> > some Linux guest booting with display on.
> > 3)  I see from boot log of  that KVM is initialized successfully, and I
> > can see /dev/kvm node.
> > 4) I built latest Qemu with --enable-kvm on this board natively.
> > 
> > What I find :
> > 1) running "qemu-system-arm  -enable-kvm   -machine vexpress-a9 ...."
> > gives error :  no accelerator found
> > 2) running "qemu-system-aarch64 -enable-kvm  -machine vexpress-a9 ...."
> > gives error : kmv_init_vcpu (IOCtl on /dev/kvm) failed, guest not supported
> > ( I experimented some modifications as well to overcome above error,
> > such as replacing value assigned to cpu->kvm_target etc, but IOCtl call
> > is failing)
> > 
> > Query:
>>  1) Does Arm64 Linux not enable KVM support for Arm32 guest ?
> > 2) Can qemu-system-arm not use the KVM feature on Arm64 host ?
> > 3) Can qemu-system-aarch64 not use KVM feature for Arm32 guest ?
> > 
> ------- Original Message -------
> Sender : Shannon Zhao<zhaoshenglong@huawei.com>
> 
> You can use below command to boot a ARM32 guest on ARM64?
> 
> qemu-system-aarch64 -enable-kvm -machine virt,kernel_irqchip=on -cpu
> host,aarch64=off ....
> 
> -- 
> Shannon


I will try above on Arm64. 

I have another query, for Arm32 host with KVM enabled.
I see that "qemu-system-arm  -enable-kvm   -machine vexpress-a9  ..." gives error
kmv_init_vcpu (IOCtl on /dev/kvm) failed, guest not supported.

Is there any way to emulate vexpress-a9  with  -enable-kvm   on qemu ?

Regards,
Ravindra Sande

Re: [Qemu-devel] [Query] Does Linux & Qemu support KVM for ARM32 guest on ARM64 host

[Peter Maydell]

On 28 April 2016 at 07:03, RAVINDRA KUMAR SANDE <r.sande@samsung.com> wrote:
> I have another query, for Arm32 host with KVM enabled.
> I see that "qemu-system-arm  -enable-kvm   -machine vexpress-a9  ..." gives error
> kmv_init_vcpu (IOCtl on /dev/kvm) failed, guest not supported.
>
> Is there any way to emulate vexpress-a9  with  -enable-kvm   on qemu ?

No. You can only emulate a CPU of the same type as the host
you're using, and the vexpress-a9 must use a Cortex-A9 CPU,
so it can't be used under virtualization.

thanks
-- PMM