[lkml]   [2008]   [Jan]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectReplacement for page fault notifiers?

the commit "x86: optimize page faults like all other achitectures and
kill notifier cruft" by Christoph Hellwig removed the page fault
notifiers (e.g. register_page_fault_notifier()) completely in 2.6.24.
Mmio-trace [1] is using them for tracking memory mapped IO, and also
other people have mentioned they need it [2,3].

This is roughly how I understand mmio-trace is working. In a loadable
kernel module calls to __ioremap() are diverted to an mmio-trace
specific function. The function calls the real __ioremap() and marks
the returned pages as not present. Access to the mapped IO memory
causes a page fault. Mmio-trace's page fault handler marks the page
present, records the event, single-steps the faulting instruction, and
finally marks the page as not present again.

- Is there anything coming to replace register_page_fault_notifier()?
- Has someone found another way to accomplish the same without patching
the kernel?
- Should I start writing a patch to bring back the notifiers, based on
the commit that removed them?

People started to complain to me that mmio-trace does not compile for
2.6.24. At least the Nouveau project is a regular user of mmio-trace
for reverse-engineering, and the tool should be easy to use. Therefore
I would prefer not to force casual contributors to patch their kernels
as it might be too much for some. I am hoping that 2.6.25, if not
2.6.24, would contain a mechanism to accomplish what I need.

I am not a subscriber, so please keep me in CC. Also I CC'd the people
who wrote about the same issue in the past.



Pekka Paalanen

 \ /
  Last update: 2008-01-08 20:53    [W:0.038 / U:4.100 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site