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

[Bhushan Bharat-R65777]

> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Friday, September 20, 2013 9:48 PM
> To: Bhushan Bharat-R65777
> Cc: Wood Scott-B07421; 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
> Subject: Re: [PATCH 5/6 v5] kvm: booke: clear host tlb reference flag on guest
> tlb invalidation
> 
> 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.

Agree

> 
> >  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.

If there is one entry then will not this be simple/faster to not lookup bitmap and guest->host array?
A flag indicate it is 1:1 map and this is physical address.

-Bharat

> 
> -Scott
>