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[PATCH v2 0/9] memory: Sanity checks memory transaction when releasing B

From: Peter Xu
Subject: [PATCH v2 0/9] memory: Sanity checks memory transaction when releasing BQL
Date: Fri, 23 Jul 2021 15:34:35 -0400

This is v2 of the series.  It was actually got forgotten for months until it
was used to identify another potential issue of bql usage here (besides it
could still be helpful when debugging a previous kvm dirty ring issue in that


So I figured maybe it's still worth to have it, hence a repost.

There're some changes against v1:

  - patch "cpus: Introduce qemu_cond_timedwait_iothread()" is dropped because
    it's introduced in another commit already (b0c3cf9407e64).

  - two more patches to move do_run_on_cpu() into softmmu/ to fix a linux-user
    compliation issue.

Please review, thanks.

=== Original Cover letter ===

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 (9):
  cpus: Export queue work related fields to cpu.h
  cpus: Move do_run_on_cpu into softmmu/cpus.c
  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: 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                  | 36 ++---------------------
 include/exec/memory-internal.h |  1 +
 include/hw/core/cpu.h          | 22 ++++++--------
 softmmu/cpus.c                 | 42 ++++++++++++++++++++++++---
 softmmu/memory.c               | 53 ++++++++++++++++++++++++++++++----
 5 files changed, 97 insertions(+), 57 deletions(-)


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