Re: [PATCH RESEND v7 9/9] tests/qtest: Fix tests when no KVM or TCG are present

[Fabiano Rosas]

Alex Bennée <alex.bennee@linaro.org> writes:

> Fabiano Rosas <farosas@suse.de> writes:
>
>> Juan Quintela <quintela@redhat.com> writes:
>>
>>> Fabiano Rosas <farosas@suse.de> wrote:
>>>> It is possible to have a build with both TCG and KVM disabled due to
>>>> Xen requiring the i386 and x86_64 binaries to be present in an aarch64
>>>> host.
>>>
>>> Ouch.
>>>
>>> Just curious: why are they needed?
>>>
>>
>> From https://wiki.xenproject.org/wiki/QEMU_Upstream:
>>
>>   Why is qemu-system-i386 used even on x86_64 and even non-x86?
>>   
>>   QEMU in a Xen system only provides device model (DM) emulation and not
>>   any CPU instruction emulation, so the nominal arch doesn't actually
>>   matter and Xen builds i386 everywhere as a basically arbitrary choice.
>>   
>>   It happens that the Xen DM part of QEMU is quite closely tied to the x86
>>   scaffolding for various historical reasons, so we end up using
>>   qemu-system-i386 even e.g. on ARM!  There is no practical difference
>>   between qemu-system-i386 and qemu-system-x86_64, they should be
>>   interchangeable. However only qemu-system-i386 is regularly tested by
>>   Xen Project (via osstest).
>
> That said with the xenpvh model that was added recently we should be
> able to finally build a Xen only qemu-system-aarch64 which while
> functionally the same will be less head scratching for users.
>

It would be nice if we could eventually restrict the x86 build to the
x86 host and the aarch64 build to the aarch64 host like we do for the
other HW accels.