Re: [PATCH] kvm/ppc/booke64: fix build breakage from Altivec, and disable e6500

[Scott Wood <scottwood@freescale.com>]

On 05/10/2013 02:06:53 PM, Caraman Mihai Claudiu-B02008 wrote:
> > > > I didn't see Tiejun's patch...  My goal was just to fix the  
> build
> > > break
> > > > without exposing problems, and to encourage a patch to fix it
> > > properly
> > > > to happen sooner rather than later.  With Tiejun's patch, which  
> is
> > > > similar to mine except that it doesn't disable e6500 support, a  
> user
> > > > could BUG() the kernel by forcing an Altivec exception in a  
> guest.
> > > I
> > > > didn't want to go further down the road of adding reflectors for
> > > those
> > > > exceptions, which could make it look like the problem was dealt  
> with
> > > > even though it's still not done.
> > >
> > > I agree it's quite annoying to hit a build breakage. Reflection  
> is not
> > > a proper solution for this problem (though we will require it  
> later)
> > > but program exception injection looks feasible as a simple fix.
> >
> > Program exception injection still doesn't deal with state  
> corruption.
> 
> Yes but it's not critical for this particular case since nobody is  
> able
> to effectively use that state via altivec instructions. Leaking state
> however can be a real issue.

Depending on guest behavior it could look like things are working even  
though they aren't (e.g. a guest just enables MSR[VEC] and uses altivec  
instructions, not relying on exceptions).  This really isn't worth  
spending a lot of time debating...  Once Altivec is fixed properly (you  
said that'd be soon, right?), we can add e6500 back to the list.

-Scott