Re: [Qemu-devel] [Qemu-arm] [PATCH 0/6] arm: support -cpu max (and gic-version=max)

[Peter Maydell <peter.maydell@linaro.org>]

On 9 December 2017 at 01:08, Eduardo Habkost <ehabkost@redhat.com> wrote:
> On Thu, Dec 07, 2017 at 07:37:31PM +0000, Peter Maydell wrote:
>> On 7 December 2017 at 18:14, Peter Maydell <peter.maydell@linaro.org> wrote:
>> > This patchset adds support for '-cpu max' to Arm, along the lines
>> > of the existing support we have for x86 targets:
>> >
>> >  * under KVM, -cpu max is the same as -cpu host
>> >  * under TCG, -cpu max means "emulate with as many features as
>> >    possible"
>>
>> Forgot to mention: -cpu max for qemu-system-aarch64 will
>> be a 64-bit cpu, and for qemu-system-arm it will be a 32-bit
>> cpu. (This differs from all the other TCG CPU types, which
>> behave the same for the 32-bit and 64-bit binaries. I think
>> it is the same way that x86 -cpu max works, though.)
>
> Are they going to be represented by two different QOM type names?
>
> (In the case of x86, all the CPU classes have different names on
> qemu-system-x86_64 and qemu-system-i386).

(Just pulling this thread up from before Christmas...)

I guess a better way to approach this would be to ask: how is
x86 implementing -cpu max, ie what is the required view of things
that I need to provide for target/arm in order to have QEMU
behave the same way x86 does? Did we write any user-facing
documentation for this feature?

(The code in this patchset makes '-cpu max' give the same
QOM type name for both qemu-system-arm and qemu-system-aarch64,
with different behaviour depending on the binary. If that means
we don't provide the same behaviour as x86 then I can change that,
but I'm not sure where the difference is exposed to the user?)

thanks
-- PMM