> > -----Original Message----- > > From: Tom Rini [mailto:trini at kernel.crashing.org] > > On Wed, Jan 12, 2005 at 08:15:08AM -0700, Tom Rini wrote: > > > On Wed, Jan 12, 2005 at 03:17:11PM +0100, Joakim Tjernlund wrote: > > > > > On Wed, Jan 12, 2005 at 08:53:17AM +0100, Joakim Tjernlund wrote: > > [snip] > > > > > > Patch looks good to me, but I want to ask when this error > > > > > > can be triggered in practice? > > > > > > > > > > It is possible to see this in the real world, as we (<hat=mvista>) > > > > > found > > > > > this with a customers app. > > > > > > > > hmm, this app must have been doing something pretty special. Any idea > > > > what > > > > caused it? > > > > > > Only vaugely. I'll poke the folks who did the investigation to see if > > > they recall (the app is quite large) and follow up with details, I hope. > > > > First, we couldn't get this issue to happen w/ anything but the custom > > app. It would generate a lot of I-TLB Error exceptions, with bit 1 of > > SRR1 set, and these went fine, the I-TLB got updated, and execution > > continued. But then at some point, and we aren't sure why exactly, an > > 0x1100 is generated, and we crash. We don't know what went and caused > > an 0x1100 to be generated instead of an 0x1300 (my wild-ass-guess is the > > code jumped very very far ahead). > > To me this looks like you entered the I-TLB Miss handler with a NULL pte which > is something that never happens in my system, don't know why this is so but I > am > guessing that the kernel populates all instruction pte's at exec time. On the > other hand I don't understand why there are so many I-TLB errors, is that > normal? > > Does the app modify its own code or construct a code trampoline which it > jumps to? Not > sure how that would be handled by the kernel w.r.t NULL pte's > > Jocke
I think I have figured this out. The first TLB misses that happen at app startup is Data TLB misses. These will then hit the NULL L1 entry and end up in do_page_fault() which will populate the L1 entry. But when you have a very large app that spans more than one L1 entry (16 MB I think) it may happen that you will have I-TLB Miss first one of the L1 entrys which will make the I-TLB handler bail out to do_page_fault() and the app craches(SEGV). Your patch will fix this. I havn't seen it go in yet, will you submit the patch to Linus/Marcelo? Jocke
