Re: [Qemu-devel] [RFC PATCH] Distinguish between reset types

[Andreas Färber]

Am 19.02.2013 12:40, schrieb David Woodhouse:
> As discussed at length already, one potential 'workaround' for KVM
> brokenness in old kernels (<3.9) with old CPUs (without 'unrestricted
> guest' support), is to properly reset the PAM registers in the chipset.
> 
> I say 'workaround' but this would be a proper fix in its own right, and
> as a side-effect would help to work around the problem we're actually
> suffering.
> 
> To do it properly, we need to distinguish between a 'hard' reset
> triggered by the PIIX3 RCR register, which resets the PAM configuration,
> and a 'soft' reset triggered for example by the keyboard controller,
> which doesn't.
> 
> This patch attempts to introduce a ResetType into the code logic. Rather
> than propagating that ResetType through the entire stack of device reset
> functions, I've added a 'qemu_last_reset_get()' function so that the
> devices which *do* care can look for it.
> 
> Comments? There are a whole bunch more qemu_system_reset_request() calls
> which will need a ResetType added, if I do it this way...

So far QEMU does not distinguish between reset types. Therefore I think
it is a bad idea to place QEMU_RESET_HARD in hw/cuda.c without reviewing
per case whether that is actually a hard or soft reset.

Better and much less intrusive would be introducing separate functions
with the new argument, leaving the existing code unchanged until
reviewed and decided by their maintainers (which may be in the range of
months). Alternatively a QEMU_RESET_DEFAULT aliased to QEMU_RESET_HARD
to raise awareness where decisions need to be taken.

Regards,
Andreas

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