Re: Running qemu-system-aarch64 with KVM support on a dual-booting android device

[Peter Maydell]

On Fri, 26 Jul 2024 at 21:07, Jonas Noll <jonas.c.noll@gmail.com> wrote:
>
> Wanted to rope everyone in here since I have forgotten to include the mailing 
> list in my reply.
>
> This worked for the main error but I continued to get the
>>
>> qemu-system-aarch64: error creating in-kernel ITS: No such device
>
> error. This was fixed with Peter's other suggestion in a private email thread:
> "The error means QEMU asked the kernel to create an ITS device,
> but it said it didn't support it. So kernel too old, or kernel
> with the ITS handling not compiled in. You can force QEMU to
> create a VM without an ITS with '-machine virt,its=off".
>
> This also worked. But naturally there's another problem now. Also not having 
> much luck finding anything on this one:

>  checking logs I found this:
>>
>> $ dmesg | grep kvm
>> [ 7197.208742]  (4)[6508:qemu-system-aar]kvm [6508]: load/store instruction 
>> decoding not implemented

This means that your guest attempted to access a device (or to
access part of the guest address space where there is no device)
using a complex load/store instruction (e.g. one with writeback,
or a multiple-register load/store). Arm virtualization support
in the CPU includes assistance for emulating simple loads and
stores, but not complex ones. KVM doesn't support trap-and-emulate
of complex load/store accesses to emulated devices, because it
would have to look at the instruction itself and decode it to
figure out what to do.

These are generally not normal kinds of load/store insn to use
on a device, so if you hit this message it tends to mean that
the guest kernel has a bug or has got confused. Occasionally
it means that the guest is doing something that would be OK
on real hardware but isn't supported by KVM -- generally the
approach there is "get the guest OS to change to not do these
odd things that don't work under virtualization".

thanks
-- PMM