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

[Philippe Mathieu-Daudé]

On 3/18/21 10:56 AM, Claudio Fontana wrote:
> 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?

But we are past soft-freeze so I'm looking for a surgical fix.

I'll send a partial revert for now.