Re: [uml-devel] [PATCH] fix writing into /dev/kmem

[Jeff Dike <jdike@addtoit.com>]

blaisorblade_spam@yahoo.it said:
> the i386 Oopses, normally, kill only the thread which triggered the
> fault -  while instead Uml panics altogether. Cannot this be changed
> at  arch/um/kernel/trap_kern.c:segv()? 

If there's an unexplained kernel mode access fault, anything could be wrong.

I don't see that it's reasonable to just kill the process when kernel data
could be corrupted as far as we know.

I don't know why x86 thinks it can just kill the process.

> By the way: in handle_page_fault(), there is some dead code (attached
> is the  removal patch).

That shouldn't be dead code.  I think it should be attached to the VM_FAULT_OOM
case - I copied it from x86, so check there to be sure.

> I also do not understand the loop around handle_mm_fault call, but I
> could be  wrong: are you sure that after a successful handle_mm_fault
> (i.e. a major or  minor fault) pte_present(*pte) could be false? If
> handle_mm_fault is not  successful, we exit the loop anyway. 

It's possible that the page could have been swapped out between fixing the
fault and the return from handle_mm_fault.  Way back in history, I had a 
check for the same fault happening twice in a row, and panicing if it happened.
This was when UML's fault handling still needed debugging.  To prevent the
case I just mentioned from triggering that panic, I added the loop to make sure
the page was good before returning to userspace.

				Jeff



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