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Date: Thu, 7 Mar 2013 10:37:47 -0600
From: Scott Wood <scottwood@freescale.com>
Subject: Re: [PATCH V4] powerpc/85xx: Add machine check handler to fix PCIe
 erratum on mpc85xx
To: Jia Hongtao-B38951 <B38951@freescale.com>
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 (from B38951@freescale.com on Thu Mar  7 02:06:05 2013)
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Cc: Wood Scott-B07421 <B07421@freescale.com>,
 David Laight <David.Laight@ACULAB.COM>,
 "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
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On 03/07/2013 02:06:05 AM, Jia Hongtao-B38951 wrote:
> Here is the ideas from Scott:
> "
> > +	if (is_in_pci_mem_space(addr)) {
> > +		inst =3D *(unsigned int *)regs->nip;
>=20
> Be careful about taking a fault here.  A simple TLB miss should be =20
> safe
> given that we shouldn't be accessing PCIe in the middle of exception
> code, but what if the mapping has gone away (e.g. a userspace driver =20
> had
> its code munmap()ed or swapped out)?  What if permissions allow =20
> execute
> but not read (not sure if Linux will allow this, but the hardware =20
> does)?
>=20
> What if it happened in a KVM guest?  You can't access guest addresses
> directly.
> "

That means you need to be careful about how you read the instruction, =20
not that you shouldn't do it at all.

-Scott=