From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <jbeulich@novell.com>
Subject: trap bounce flags
Date: Wed, 25 Apr 2007 10:56:36 +0100
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To: Ian Campbell <Ian.Campbell@XenSource.com>, Keir Fraser <keir@XenSource.com>
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With the severe stability issues we are having with SLE10sp1 on x86-64, =
things
start pointing pretty closely at the int80 direct trap patch we imported =
from
-unstable. While I just now realized that there's been a fix for these =
problems
for quite a while (don't know how this slipped my attention), I still have =
a few
notes:

- even compat_restore_all_guest now asserts interrupts are disabled, =
despite
  32-bit restore_all_guest not doing so (and the iret path not generally =
needing
  this)
- int80_direct_trap checks for non-zero TRAPBOUNCE_flags, yet
  {,compat_}create_bounce_frame clear the low byte of these flags (i.e.
  including TBF_exception, which is in this lower byte); it appears to be =
only a
  lucky coincidence that this still works as the cmp (again!) is suffix-les=
s and
  hence gets sized as a 32-bit compare, accidentally covering TRAPBOUNCE_cs=

- from the above, why is it that only the lower byte (if anything) needs =
clearing?

Jan