Re: [PATCH kvm-unit-tests] arm: fix crash when caches are off

[Andrew Jones <drjones@redhat.com>]

On Fri, Sep 26, 2014 at 09:51:15AM +0200, Christoffer Dall wrote:
> On Tue, Sep 16, 2014 at 08:57:31AM -0400, Andrew Jones wrote:
> > 
> > 
> > ----- Original Message -----
> > > Il 16/09/2014 14:43, Andrew Jones ha scritto:
> > > > I don't think we need to worry about this case. AFAIU, enabling the
> > > > caches for a particular cpu shouldn't require any synchronization.
> > > > So we should be able to do
> > > > 
> > > >     enable caches
> > > >     spin_lock
> > > >     start other processors
> > > >     spin_unlock
> > > 
> > > Ok, I'll test and apply your patch then.
> > > 
> > > Once you change the code to enable caches, please consider hanging on
> > > spin_lock with caches disabled.
> > 
> > Unfortunately I can't do that without changing spin_lock into a wrapper
> > function. Early setup code calls functions that use spin_locks, e.g.
> > puts(), and we won't want to move the cache enablement into early setup
> > code, as that should be left for unit tests to turn on off as they wish.
> > Thus we either need to be able to change the spin_lock implementation
> > dynamically, or just leave the test/return as is.
> > 
> My take on this whole thing is that we're doing something fundamentally
> wrong.  I think what we should do is to always enable the MMU for
> running actual tests, bringing up multiple CPUs etc.  We could have an
> early_printf() that doesn't use the spinlock.  I think this will just be
> a more stable setup.
> 
> Do we have clear ideas of which kinds of tests it would make sense to
> run without the MMU turned on?  If we can be more concrete on this
> subject, perhaps a special path (or build) that doesn't enable the MMU
> for running the aforementioned test cases could be added.
> 

Finally carving out kvm-unit-tests time again and fixed this properly.
A series is on the list "[kvm-unit-tests PATCH 0/6] arm: enable MMU".

drew