Re: [patch 0/6] Strong Access Ordering page attributes for POWER7

Dave Kleikamp
2008-07-07T14:05:42Z

On Fri, 2008-07-04 at 09:39 +1000, Benjamin Herrenschmidt wrote:
> On Wed, 2008-06-18 at 17:32 -0500, shaggy@linux.vnet.ibm.com wrote:
> > Andrew,
> >
> > The first patch in this series hits architecture independent code, but the
> > rest is contained in the powerpc subtree. Could you pick up the first
> > patch into -mm? I can send the rest of them through the powerpc git tree.
> > The first patch and the rest of the set are independent and can be merged
> > in either order.
>
> ../..
>
> I was wondering... how do we inform userspace that this is available ?
> Same question with adding the endian bit on 4xx which I plan to do using
> your infrastructure...

I hadn't really given it much thought. Is there a simple way to
determine if the cpu is power 7 or newer?

It's not elegant, but a program could call mmap() with PROT_SAO set and
check for errno == EINVAL. Then call again without PROT_SAO, if it
needs to.

> We haven't defined a user-visible feature bit (and besides, we're really
> getting short on these...). This is becoming a bit of concern btw (the
> running out of bits). Maybe we should start defining an AT_HWCAP2 for
> powerpc and get libc updated to pick it up ?

Joel,
Any thoughts?

Shaggy
--
David Kleikamp
IBM Linux Technology Center