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

[Scott Wood <scottwood@freescale.com>]

On 05/10/2013 02:15:34 PM, Scott Wood wrote:
> 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.

Am I going to see an Altivec patch soon, or should I ask Gleb to take  
this patch instead?

-Scott