Kernel related (?) user space crash at ARM11 MPCore
Russell King - ARM Linux
linux at arm.linux.org.uk
Wed Sep 23 08:42:38 EDT 2009
On Wed, Sep 23, 2009 at 02:12:23PM +0200, Mikael Pettersson wrote:
> Catalin Marinas writes:
> > On Wed, 2009-09-23 at 10:13 +0100, Catalin Marinas wrote:
> > > 1. The patch I just posted which introduces flush_prot_range(). It
> > > affects generic code but if people here agree with the idea, I'm
> > > happy to try to push for it upstream. It allows mprotect(rx) to
> > > flush the caches as some people might expect and doesn't affect
> > > the fork or mmap performance
> > > 2. Russell's (unposted) patch (or the one above) for flushing the
> > > D-cache during CoW (no I-cache invalidation necessary). There
> > > would be a (probably slight) performance drop for applications
> > > using intensive forking (apache?) but it shouldn't be that
> > > different from read-allocate caches. The common fork+exec
> > > combination shouldn't do much CoW so I don't expect this to be
> > > affected
> > > 3. My initial patch for flush_cache_range but it would be better to
> > > disable read-implies-exec
> > > 4. Handle the prefetch abort for exec permission and only to the
> > > flushing there (this patch would be a bit more complicated)
> > I did some tests with OABI_COMPAT disabled so that read-implies-exec is
> > also disabled. Option 3 above has no noticeable performance drop
> > compared to a vanilla kernel, also with OABI_COMPAT disabled.
> > Which would make me recommend workaround 3 if OABI compatibility is not
> > required. I'm not sure what Debian or Ubuntu do (I think the latter has
> > OABI_COMPAT disabled). If OABI is required, we should go with 2.
> > I've spent too much time already on this issue. There are several
> > solutions available, all with drawbacks. If there are no other solutions
> > to be proposed (other than modifying user-space), maybe we should vote
> > on the favourite option.
> > My vote: 2 (until we no longer have OABI filesystems around)
> OABI is obsolete legacy, so while it should (perhaps) be
> kept working, it should not be allowed to negatively affect
> the performance of pure EABI systems.
> If option 3 is best for EABI then that's my vote.
However, Catalins benchmarks don't include testing my patch with EABI
executables with RIX disabled, so we really don't know how it would
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