[Qemu-devel] [PATCH v2 for-2.11 0/2] Fix TCG atomic writes to nondirty pages

From: Peter Maydell <peter.maydell@linaro.org>
To: qemu-devel@nongnu.org
Cc: qemu-stable@nongnu.org, Richard Henderson <rth@twiddle.net>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Stuart Monteith <stuart.monteith@linaro.org>
Subject: [Qemu-devel] [PATCH v2 for-2.11 0/2] Fix TCG atomic writes to nondirty pages
Date: Mon, 20 Nov 2017 18:08:26 +0000	[thread overview]
Message-ID: <1511201308-23580-1-git-send-email-peter.maydell@linaro.org> (raw)

To do a write to memory that is marked as notdirty, we need
to invalidate any TBs we have cached for that memory, and
update the cpu physical memory dirty flags for VGA and migration.
The slowpath code in notdirty_mem_write() does all this correctly,
but the new atomic handling code in atomic_mmu_lookup() doesn't
do anything at all, it just clears the dirty bit in the TLB.

The effect of this bug is that if the first write to a notdirty
page for which we have cached TBs is by a guest atomic access,
we fail to invalidate the TBs and subsequently will execute
incorrect code. This can be seen by trying to run 'javac' on AArch64.

The first patch here refactors notdirty_mem_write() to pull out
the "correctly handle dirty bit updates" parts of the code into
two new functions memory_notdirty_write_prepare() and
memory_notdirty_write_complete(). The second patch then uses
those functions to fix the atomic helpers.

Changes v1->v2:
 * add the 'bool active;' flag to NotDirtyInfo in patch 1
 * change the comment on NotDirtyInfo in patch 1 to document
   the active flag (and to fix incorrect references to function
   names that I forgot to update when I decided on the names for
   the prepare/complete functions)
 * in patch 2, don't call prepare unless the TLB was notdirty
 * in patch 2, use the active flag to track whether we need to
   call complete or not

thanks
-- PMM

Peter Maydell (2):
  exec.c: Factor out before/after actions for notdirty memory writes
  accel/tcg: Handle atomic accesses to notdirty memory correctly

 accel/tcg/atomic_template.h    | 12 ++++++++
 include/exec/memory-internal.h | 62 ++++++++++++++++++++++++++++++++++++++++
 accel/tcg/cputlb.c             | 38 +++++++++++++++---------
 accel/tcg/user-exec.c          |  1 +
 exec.c                         | 65 ++++++++++++++++++++++++++++--------------
 5 files changed, 144 insertions(+), 34 deletions(-)

-- 
2.7.4