Re: [Qemu-devel] i386: pc: align gpa<->hpa on 1GB boundary (v4)

[Marcelo Tosatti <mtosatti@redhat.com>]

On Thu, Nov 07, 2013 at 12:15:59AM +0200, Michael S. Tsirkin wrote:
> On Wed, Nov 06, 2013 at 07:53:51PM -0200, Marcelo Tosatti wrote:
> > On Wed, Nov 06, 2013 at 11:40:34PM +0200, Michael S. Tsirkin wrote:
> > > On Wed, Nov 06, 2013 at 07:31:19PM -0200, Marcelo Tosatti wrote:
> > > > 
> > > > v2: condition enablement of new mapping to new machine types (Paolo)
> > > > v3: fix changelog
> > > > v4: rebase
> > > > 
> > > > -----
> > > > 
> > > > 
> > > > Align guest physical address and host physical address
> > > > beyond guest 4GB on a 1GB boundary.
> > > > 
> > > > Otherwise 1GB TLBs cannot be cached for the range.
> > > > 
> > > > Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> > > 
> > > Um. This will conflict with:
> > >     pc: map PCI address space as catchall region for not mapped addresses
> > > 
> > > I think we really should stop using the hacked hole thing
> > > and just use priorities like that patch does.
> > 
> > Sorry hacked in what way?
> > This patch is necessary to enable 1GB hugepages beyond 4GB of RAM on the
> > current machine types.
> 
> 
> Sorry if I wasn't clear. when I said "hacked" I was talking about the
> pci hole concept generally in upstream qemu, not about your patch.
> 
> Its hacked because there's no "pci hole" on PIIX.
> pci hole is where pci was hiding some ram behind it
> on some systems. AFAIK this is not what is happens on piix though.
> What happens really is that everything not covered by RAM memory is PCI.
> 
> We implemented this using two aliases of RAM but
> the natural thing is really just making PCI lower
> priority than RAM and let it overlap.
>
> > > Do you agree? If yes I'm afraid your patch will have to be
> > > rebased on top of that yet again, sorry to give you a
> > > run-around like that :(
> > 
> > I don't see what exactly is the suggestion (or why the proposed 
> > patch should conflict with "pc: map PCI address space as catchall region
> > for not mapped addresses").
> 
> It seemed to me that they will conflict but it's after midnight
> so maybe I'm confused.
> You are saying you apply yours on top and there's no conflict?
> In that case I'll recheck, sorry.

No conflict between "pc: map PCI address space as catchall region" 
and the proposed patch.

> > > Also - do you think this is 1.7 material?
> > 
> > No. Paolo mentioned you have a tree with 1.8 material, correct?
> 
> Yes
> 
> git://git.kernel.org/pub/scm/virt/kvm/mst/qemu.git pci