[16:29] <manjo> kamal__, looks like you backported ARM: fix alignment of keystone page table fixup do you recall what issue this fixed ?
[16:33] <apw> manjo, from the description i'd say it makes sure the end of the kernel data space is mapped properly, which i would to mean random builds working and randoms ones not
[16:34] <manjo> apw, ok I have a similar situation ... so was trying to understand that patch
[16:35] <manjo> apw, was looking for any bug report so that I can compare the trace 
[16:35] <manjo> apw, the bug that it ref to is of no help 
[16:35] <apw> the bug would be a stable being applied en-toto bug i assume
[16:35] <apw> the original is no more verbose, and has no bug associated
[16:36] <manjo> bah
[16:36] <apw> but as it is random end of data space alignment issues, it woud literally be anything that happens to be linked there which would be missing
[16:36] <kamal__> manjo, yeah, that commit was just "cc: stable", hence I merged it...  there is/was no bug reference for it.
[16:36] <apw> i doubt it is constrained to any particular thing
[16:36] <manjo> apw, so in my case a dkms module does a get_user_pages() but it is unable to pin it because *pmd = 00000000
[16:37] <manjo> kamal__, ack I feard that might be the case
[16:37] <manjo> but the code worked in a previous build but no in the current build 
[16:39] <apw> manjo, have you a crash stack for it?
[16:40] <manjo> pmed you the bug 
[16:48] <apw> that stack could just be saying you asked it to map something from userspace which does not exist
[16:49] <manjo> right so it seems like there is nothing wrong kernel wise ... but the user tells me that they did not see failures like this before 
[16:50] <apw> that tells you nothing other than they used to be luckier, in reality.  code which should and indeed seems impossible to have worked ever
[16:50] <apw> often works for years before exploding and showing you they are passing the wrong thing
[16:51] <manjo> did you see my comment #2 ? that is what I was trying to understand as to why their module is trying to pin invalid page table
[16:52] <apw> well that is simply defined by the address you pass in, it is saying "you asked me to pin a page in this range, but there isn't even a pmd for it, so there is no page EFAULT"
[16:52] <manjo> I want to completely rule out that any merge from ubuntu to this flavor kernel did not intro any regressions
[16:53] <apw> from that trace, i would say the driver reported that the get_user_pages failed, and then went on to use the address anyhow as if it did not
[16:55] <manjo> :) yeah it looks messed up ... trying to untangle the spaghetti so that I can put the ball on their court