Re: kvm_amd BUG: unable to handle kernel NULL pointer dereference at 00000014

["Roedel, Joerg" <Joerg.Roedel@amd.com>]

On Mon, Mar 07, 2011 at 07:50:14AM -0500, Avi Kivity wrote:
> On 03/07/2011 02:11 PM, Roedel, Joerg wrote:

> > There is no access to per_cpu variables at the start of x86_decode_insn.
> > I did a bit of investigation and it turns out that the faulting
> > instruction is inserted into the code by the gcc because the
> > CONFIG_CC_STACKPROTECTOR is enabled.
> > The user tested this is Ubuntu 11.04 alpha-something i386 and this
> > distro uses gcc 4.5.2. So CC_STACKPROTECTOR seems to be harmful with
> > this gcc version but I am not sure whether this counts as a gcc bug.
> 
> Ah, looks like %gs is the expected segment on i386 with 
> -fstack-protector.  So we must disable lazy gs reload in that scenario.

According to the comments in stackprotector.h its the same on amd64 (the
difference is that gcc expects the canary value at a different offset
from %gs).
So we should probably unlazy %gs reload alltogether.

	Joerg

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