Date: Mon, 19 Nov 2007 18:05:16 +0100
Message-ID: <s5hlk8ujhdf.wl%tiwai@suse.de>
From: Takashi Iwai <tiwai@suse.de>
To: Zachary Amsden <zach@vmware.com>
Cc: Christoph Hellwig <hch@infradead.org>,
       Jeremy Fitzhardinge <jeremy@goop.org>,
       Tobias Powalowski <t.powa@gmx.de>, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] x86/paravirt: revert exports to restore old behaviour
In-Reply-To: <1195001464.6352.109.camel@bodhitayantram.eng.vmware.com>
References: <200711131139.42791.t.powa@gmx.de>
	<473A073C.2020201@goop.org>
	<20071113222212.GA1322@infradead.org>
	<1195001464.6352.109.camel@bodhitayantram.eng.vmware.com>
User-Agent: Wanderlust/2.15.5 (Almost Unreal) SEMI/1.14.6 (Maruoka)
 FLIM/1.14.7 (=?ISO-8859-4?Q?Sanj=F2?=) APEL/10.6 MULE XEmacs/21.5 (beta28)
 (fuki) (+CVS-20070806) (i386-suse-linux)
MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka")
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2385
Lines: 56

At Tue, 13 Nov 2007 16:51:04 -0800,
Zachary Amsden wrote:
> 
> On Tue, 2007-11-13 at 22:22 +0000, Christoph Hellwig wrote:
> > On Tue, Nov 13, 2007 at 12:21:16PM -0800, Jeremy Fitzhardinge wrote:
> > > Subject: 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.
> > 
> > NACK, both of these are internal and graphics drivers should not be
> > using them.
> 
> Some of them are internal, but some are not, they just happened to be
> privileged CPU operations available to anyone.
> 
> Does anyone know what hooks they are actually using?  Something like
> reading MSRs is not internal at all, it is CPU specific, and the
> graphics drivers might have very good reasons to read them to figure out
> how AGP is configured for example.
> 
> The graphics drivers most certainly don't need to be paravirtualized
> however, so they could always work around this with raw asm constructs.
> 
> The mmu_ops hook is more debatable.  But until someone figures out what
> hooks they want, we can't know whether they are internal or not.  In any
> case, this is a regression.

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.

The easiest workaround I found was to undefine CONFIG_PARAVIRT before
inclusion of linux kernel headers, but it is really ugly and hacky.
Redefinig with raw_*() and native_*() is another way, but it takes
much more work than defining these primitive functions in assembly.

So, in short, with EXPORT_SYMBOL_GPL change, it's pretty hard to write
a non-GPL driver in a same manner...


Takashi
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/