[PATCH 5/6 v5] kvm: booke: clear host tlb reference flag on guest tlb invalidation

[Scott Wood]

On Thu, 2013-09-19 at 23:19 -0500, Bhushan Bharat-R65777 wrote:
> 
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Friday, September 20, 2013 2:38 AM
> > To: Bhushan Bharat-R65777
> > Cc: benh at kernel.crashing.org; agraf at suse.de; paulus at samba.org;
> > kvm at vger.kernel.org; kvm-ppc at vger.kernel.org; linuxppc-dev at lists.ozlabs.org;
> > Bhushan Bharat-R65777
> > Subject: Re: [PATCH 5/6 v5] kvm: booke: clear host tlb reference flag on guest
> > tlb invalidation
> > 
> > This breaks when you have both E500_TLB_BITMAP and E500_TLB_TLB0 set.
> 
> I do not see any case where we set both E500_TLB_BITMAP and
> E500_TLB_TLB0.

This would happen if you have a guest TLB1 entry that is backed by some
4K pages and some larger pages (e.g. if the guest maps CCSR with one big
TLB1 and there are varying I/O passthrough regions mapped).  It's not
common, but it's possible.

>  Also we have not optimized that yet (keeping track of
> multiple shadow TLB0 entries for one guest TLB1 entry)

This is about correctness, not optimization.

> We uses these bit flags only for TLB1 and if size of stlbe is 4K then
> we set E500_TLB_TLB0  otherwise we set E500_TLB_BITMAP. Although I
> think that E500_TLB_BITMAP should be set only if stlbe size is less
> than gtlbe size.

Why?  Even if there's only one bit set in the map, we need it to keep
track of which entry was used.

-Scott