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

On 20/11/2017 19:08, Peter Maydell wrote:
> 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.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks!

Paolo

> 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(-)
> 

On 20 November 2017 at 20:54, Paolo Bonzini <pbonzini@redhat.com> wrote:
> On 20/11/2017 19:08, Peter Maydell wrote:
>> 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.
>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks; applied to master for rc2.

-- PMM