[PATCH] ARM: Add PI/robust mutexes support for SMP kernels

[cbouatmailru@gmail.com (Anton Vorontsov)]

On Mon, Jun 07, 2010 at 09:56:10PM +0100, Catalin Marinas wrote:
> On Mon, 2010-06-07 at 20:44 +0100, Russell King - ARM Linux wrote:
> > On Mon, Jun 07, 2010 at 09:36:30PM +0400, Anton Vorontsov wrote:
> > > To support PI or robust mutexes, the kernel needs to perform some
> > > operations atomically on userspace addresses, and yet ARM lacked
> > > the support for the SMP case.
> > >
> > > ARMv6 adds exclusive access variants of ldr and str instructions,
> > > which means that support for PI/robust mutexes should now be
> > > relatively straightforward.
> > 
> > It isn't this straight forward.  You're now bypassing the MMU protections
> > in that 'strex' can bypass the read-only protection of the user page.
> > This can result in the zero BSS page being corrupted, or worse corruption
> > to page cache pages.
> 
> Do you mean STREX in SVC mode targeting user pages? I keep posting a
> patch for more than a year :) which removes the domains switching and
> makes user pages read-only for both kernel and user space.

Wow. Then I should just make PI/robust mutexes depend on
!CONFIG_CPU_USE_DOMAINS (which is actually always true for SMP :-).

Thanks!

-- 
Anton Vorontsov
email: cbouatmailru at gmail.com
irc://irc.freenode.net/bd2