On 03/14/2013 09:47:58 PM, Jia Hongtao-B38951 wrote:

=20

quoted

-----Original Message-----
From: Wood Scott-B07421
Sent: Thursday, March 14, 2013 12:38 AM
To: David Laight
Cc: Jia Hongtao-B38951; Wood Scott-B07421; =20

linuxppc-dev@lists.ozlabs.org;

quoted

Stuart Yoder
Subject: Re: [PATCH V4] powerpc/85xx: Add machine check handler to =20

fix

quoted

PCIe erratum on mpc85xx

On 03/13/2013 04:40:40 AM, David Laight wrote:

quoted

quoted

Hmm, seems there's no probe_user_address() -- for userspace we
basically want the same thing minus the KERNEL_DS.  See
arch/powerpc/perf/callchain.c for an example.

Isn't that just copy_from_user() ?

Plus pagefault_disable/enable().

-Scott

=20
pagefault_disable() is identical to preempt_disable(). So I think this
could not avoid other cpu to swap out the instruction we want to read =20
back.
probe_kernel_address() also have the same issue.

That's not the point -- the point is to let the page fault handler know =20
that it should go directly to bad_page_fault().  Do not pass =20
handle_mm_fault().  Do not collect a page from disk.

Granted, we're already in atomic context which will have that effect =20
due to being in the machine check handler, but it's better to be =20
explicit about it and not depend on how pagefault_diasble() is =20
implemented.

-Scott=