-----Original Message-----
From: Wood Scott-B07421
Sent: Friday, March 08, 2013 12:38 AM
To: Jia Hongtao-B38951
Cc: David Laight; Wood Scott-B07421; linuxppc-dev@lists.ozlabs.org;
Stuart Yoder
Subject: Re: [PATCH V4] powerpc/85xx: Add machine check handler to fix
PCIe erratum on mpc85xx
=20
On 03/07/2013 02:06:05 AM, Jia Hongtao-B38951 wrote:

quoted

Here is the ideas from Scott:
"

quoted

+	if (is_in_pci_mem_space(addr)) {
+		inst =3D *(unsigned int *)regs->nip;

Be careful about taking a fault here.  A simple TLB miss should be
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 had its code munmap()ed or swapped out)?  What if
permissions allow execute but not read (not sure if Linux will allow
this, but the hardware does)?

What if it happened in a KVM guest?  You can't access guest addresses
directly.
"

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

I agree.

Do you have a more secure way to get the instruction?
Or what should be done to avoid permission break issue?

Thanks.
-Hongtao