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Subject[PATCH] 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.

Tobias Powalowski <t.powa@gmx.de> reports:
> commit to .24 tree:
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=93b1eab3d29e7ea32ee583de3362da84db06ded8
>
> introduces:
> +EXPORT_SYMBOL_GPL(pv_mmu_ops);
> +EXPORT_SYMBOL_GPL(pv_cpu_ops);
>
> pv_cpu_ops is for nvidia
> pv_mmu_ops' is for amd(ati)
>
> which will break 32bit systems with paravirt enabled and trying to compile
> the binary graphic drivers from amd(ati) and nvidia.

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>

---
arch/x86/kernel/paravirt_32.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff -r 0328c71b880c arch/x86/kernel/paravirt_32.c
--- a/arch/x86/kernel/paravirt_32.c Tue Nov 27 11:21:09 2007 -0800
+++ b/arch/x86/kernel/paravirt_32.c Tue Nov 27 11:21:16 2007 -0800
@@ -465,8 +465,8 @@ struct pv_mmu_ops pv_mmu_ops = {
};

EXPORT_SYMBOL_GPL(pv_time_ops);
-EXPORT_SYMBOL_GPL(pv_cpu_ops);
-EXPORT_SYMBOL_GPL(pv_mmu_ops);
+EXPORT_SYMBOL (pv_cpu_ops);
+EXPORT_SYMBOL (pv_mmu_ops);
EXPORT_SYMBOL_GPL(pv_apic_ops);
EXPORT_SYMBOL_GPL(pv_info);
EXPORT_SYMBOL (pv_irq_ops);
-
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