Terence Ripperda <[email protected]> writes:
> this appears to be the 'vmalloc guard page causing change_page_attr
> problems' bug. at one point, iounmap subtracted the guard page before
> calling change_page_attr, but I see this was reverted as part of a
> recent cleanup.
Hmm, yes looks like it was reintroduced.
> from looking at the implementation in 2.6.12-pre4, I'm not clear how
I suppose you mean rc4, not pre4?
> the guard page is accounted for in iounmap. in vmalloc.c, the guard
> page is subtracted from the vm_struct in remove_vm_area (which calls
> unmap_vm_area). but iounmap in ioremap.c calls unmap_vm_area directly
> rather than calling remove_vm_area, so the guard page is never
> subtracted and the wrong size is passed to change_page_attr.
Ok obviously needs to be fixed.
>
> is the intent that iounmap should call remove_vm_area rather than
> unmap_vm_area (with additional changes to not unlink the vma itself)?
> or that the guard page should be removed by unmap_ rather than
> remove_?
There doesn't seem to be a clear rule, that is where the confusion
comes from I guess. I would consider it cleaner to handle it in
the higher level vmalloc code.
>
> when debugging this issue, I also ran into problems with iounmap using
> virt_to_page on a pci IO region. this problem went away when I tried
> calling change_page_attr_addr with the virtual address instead. but
A patch for that already went into mainline.
> perhaps iounmap should be calling ioremap_change_attr rather than
What is ioremap_change_attr?
> change_page_attr directly. I'll run some additional tests and send out
> a patch.
-Andi
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