tree 96edbfcd901873c7c3094f9829d2db436fba269a
parent b8415ec34fd63c6260497b2f8aaf3ce7a61eaa8a
author Jeremy Fitzhardinge <jeremy@goop.org> 1196295731 -0800
committer Linus Torvalds <torvalds@woody.linux-foundation.org> 1196357095 -0800

x86/paravirt: revert exports to restore old behaviour

Subdividing the paravirt_ops structure caused a regression in certain
non-GPL modules which try to use mmu_ops and cpu_ops.  This restores the
old behaviour, and makes it consistent with the non-CONFIG_PARAVIRT case.

Takashi Iwai <tiwai@suse.de> adds:
> I took at this problem (as I have an nvidia card on one of my
> workstations), and found out that the following suffer from
> EXPORT_SYMBOL_GPL changes:
>
> * local_disable_irq(), local_irq_save*(), etc.
> * MSR-related macros like rdmsr(), wrmsr(), read_cr0(), etc.
>   wbinvd(), too.
> * pmd_val(), pgd_val(), etc are all involved with pv_mm_ops.
>   pmd_large() and pmd_bad() is also indirectly involved.
>   __flush_tlb() and friends suffer, too.

Christoph Hellwig objects to this patch on the grounds that modules
shouldn't be using these operations anyway.  I don't think this is a
particularly good reason to reject the patch, for several reasons:

1. These operations are still available to modules when not using
   CONFIG_PARAVIRT, since they are implicitly exported as inline
   functions via the kernel headers.  Exporting the same functionality as
   GPL-only symbols just adds a gratuitious difference between
   CONFIG_PARAVIRT and non-CONFIG_PARAVIRT configurations.  If we really
   think these operations are not for module use (or non-GPL module use),
   then we should solve the problem in a general way.

2. It's a regression from previous kernels, which would work these
   modules even with CONFIG_PARAVIRT enabled.

3. The operations in question seem pretty reasonable for modules to
   use.  The control registers/MSRs can be accessed directly anyway, so there's
   no benefit in preventing modules from using standard interfaces.  And it seems
   reasonable to allow a graphics driver to create its own mappings if it wants.

Therefore, I think this patch should go in for 2.6.24.  If people
really think that these operations should not be available to modules,
then we can address that separately.

Signed-off-by: Jeremy Fitzhardinge <Jeremy.Fitzhardinge@citrix.com>
Cc: Tobias Powalowski <t.powa@gmx.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Takashi Iwai <tiwai@suse.de>
Cc: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>