Re: [PATCH v2 3/3] target/arm: Restrict v7A TCG cpus to TCG accel

[Claudio Fontana]

On 3/18/21 10:47 AM, Philippe Mathieu-Daudé wrote:
> Hi Peter,
> 
> On 3/11/21 11:43 AM, Claudio Fontana wrote:
>> On 2/21/21 11:26 PM, Philippe Mathieu-Daudé wrote:
>>> KVM requires the target cpu to be at least ARMv8 architecture
>>> (support on ARMv7 has been dropped in commit 82bf7ae84ce:
>>> "target/arm: Remove KVM support for 32-bit Arm hosts").
>>>
>>> A KVM-only build won't be able to run TCG cpus, move the
>>> v7A CPU definitions to cpu_tcg.c.
>>>
>>> Reported-by: Peter Maydell <peter.maydell@linaro.org>
>>> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
>>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>>
>>
>> Here I think it's better to keep the "a15" cpu around,
>> until we fix the board configuration situation.
>>
>> I added a patch that does that into my KVM-only build series, to avoid the 
>> resulting breakages.
> 
> Actually I got a downstream report that this break migration from QEMU
> 5.2 to QEMU 6.0.
> 
> I first thought it was on an old kernel (with 32-bit KVM enabled),
> but not, it is for Aarch64 VMs on recent KVM (without 32-bit support)
> but the 'virt' machines were started with default Cortex-A15 CPU...
> 
>     mc->default_cpu_type = ARM_CPU_TYPE_NAME("cortex-a15");
> 
> I'm not sure upstream should care about this case, but I though
> maybe you could give me hints about the best way to keep old VMs
> working, as this likely affects any distribution. Obviously not
> upgrading QEMU is not a solution :)
> 
> The simplest seems to revert 82bf7ae84ce and this patch, but I
> doubt this will be enough.
> 
> Maybe there is some clever thing to do before reverting 82bf7ae84ce,
> that could also benefit upstream, by doing something with versioned
> machines? I have no idea (yet) how that work and if it could work.

Does just applying my series fix it?

https://lists.gnu.org/archive/html/qemu-devel/2021-03/msg06463.html

Ie, I have resurrected specifically the a15 to keep things working for "virt".

Patch 22/50. Maybe I am missing something though?

https://lists.gnu.org/archive/html/qemu-devel/2021-03/msg06494.html

Ciao,

Claudio