Re: [PATCH 1/2] cpu: Do not reset a vCPU before it is created

[Laurent Vivier]

Le 09/03/2020 à 14:18, Peter Maydell a écrit :
> On Mon, 9 Mar 2020 at 13:13, Laurent Vivier <address@hidden> wrote:
>>
>> Le 09/03/2020 à 14:09, Peter Maydell a écrit :
>>> On Mon, 9 Mar 2020 at 12:11, Philippe Mathieu-Daudé <address@hidden> wrote:
>>>>
>>>> cpu_reset() might modify architecture-specific fields allocated
>>>> by qemu_init_vcpu(). To avoid bugs similar to the one fixed in
>>>> commit 00d0f7cb66 when introducing new architectures, move the
>>>> cpu_reset() calls after qemu_init_vcpu().
>>>>
>>>> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
>>>
>>> Why do we need to call cpu_reset() from realize anyway?
>>> Generally for devices this is incorrect as they should be
>>> being reset by some other mechanism.
>>
>> I have this same change in my branch for q800 to set the initial PC and
>> stack pointer read from memory on cold boot.
>>
>> Do we have another way to do that?
> 
> The expectation at the moment is that the board code should
> register a reset function with qemu_register_reset() which
> calls cpu_reset(). Relying on doing a reset in realize won't
> work for the case where there's a QEMU system reset, because
> we don't re-init/realize everything, we just call all the
> reset hooks.
> 
> If m68k reads pc/sp from memory on reset you'll probably run
> into the same reset-ordering vs hw/cpu/loader.c that Arm M-profile
> has; we currently work around that in the arm reset function.
> I had hoped that 3-phase reset would resolve this reset order
> issue, but it has not turned out to be so easy.


Thank you for the hint, I'll have a look.

Laurent