This is a continuous work of previous discussion on memory transactions [1].
It should be helpful to fail QEMU far earlier if there's misuse of BQL against
the QEMU memory model.

One example is run_on_cpu() during memory commit.  That'll work previously, but
it'll fail with very strange errors (like KVM ioctl failure due to memslot
already existed, and it's not guaranteed to trigger constantly).  Now it'll
directly fail when run_on_cpu() is called.

Please have a look, thanks.

[1] https://lists.gnu.org/archive/html/qemu-devel/2020-04/msg03205.html

Peter Xu (8):
  memory: Introduce memory_region_transaction_{push|pop}()
  memory: Don't do topology update in memory finalize()
  cpus: Use qemu_cond_wait_iothread() where proper
  cpus: Introduce qemu_cond_timedwait_iothread()
  cpus: Remove the mutex parameter from do_run_on_cpu()
  cpus: Introduce qemu_mutex_unlock_iothread_prepare()
  memory: Assert on no ongoing memory transaction before release BQL
  memory: Delay the transaction pop() until commit completed

 cpus-common.c                  |  5 ++--
 cpus.c                         | 32 ++++++++++++++------
 include/exec/memory-internal.h |  1 +
 include/hw/core/cpu.h          |  4 +--
 include/qemu/main-loop.h       |  7 +++++
 memory.c                       | 53 ++++++++++++++++++++++++++++++----
 6 files changed, 81 insertions(+), 21 deletions(-)

-- 
2.24.1

On Tue, Apr 21, 2020 at 12:21:00PM -0400, Peter Xu wrote:
> This is a continuous work of previous discussion on memory transactions [1].
> It should be helpful to fail QEMU far earlier if there's misuse of BQL against
> the QEMU memory model.
> 
> One example is run_on_cpu() during memory commit.  That'll work previously, but
> it'll fail with very strange errors (like KVM ioctl failure due to memslot
> already existed, and it's not guaranteed to trigger constantly).  Now it'll
> directly fail when run_on_cpu() is called.
> 
> Please have a look, thanks.
> 
> [1] https://lists.gnu.org/archive/html/qemu-devel/2020-04/msg03205.html

Still think it as something good to have...  Any comments?  Thanks,

-- 
Peter Xu