From: Miguel Luis <miguel.l...@oracle.com> [BROKEN: This patch is just for reference. It has problems as it does not takes care of the TranslationBlocks and their assigned regions during CPU unrealize]
When using TCG acceleration in a multi-threaded context each vCPU has its own thread registered in tcg_ctxs[] upon creation and tcg_cur_ctxs stores the current number of threads that got created. Although, the lack of a mechanism to unregister these threads is a problem when exercising vCPU hotplug/unplug due to the fact that tcg_cur_ctxs gets incremented everytime a vCPU gets hotplugged but never gets decremented everytime a vCPU gets unplugged, therefore breaking the assert stating tcg_cur_ctxs < tcg_max_ctxs after a certain amount of vCPU hotplugs. Suggested-by: Salil Mehta <salil.me...@huawei.com> [SM: Check Things To Do Section, https://lore.kernel.org/all/20200613213629.21984-1-salil.me...@huawei.com/] Signed-off-by: Miguel Luis <miguel.l...@oracle.com> --- accel/tcg/tcg-accel-ops-mttcg.c | 1 + include/tcg/startup.h | 7 +++++++ tcg/tcg.c | 24 ++++++++++++++++++++++++ 3 files changed, 32 insertions(+) diff --git a/accel/tcg/tcg-accel-ops-mttcg.c b/accel/tcg/tcg-accel-ops-mttcg.c index c552b45b8e..b6d7911a87 100644 --- a/accel/tcg/tcg-accel-ops-mttcg.c +++ b/accel/tcg/tcg-accel-ops-mttcg.c @@ -122,6 +122,7 @@ static void *mttcg_cpu_thread_fn(void *arg) bql_unlock(); rcu_remove_force_rcu_notifier(&force_rcu.notifier); rcu_unregister_thread(); + tcg_unregister_thread(); return NULL; } diff --git a/include/tcg/startup.h b/include/tcg/startup.h index f71305765c..dc35b24de5 100644 --- a/include/tcg/startup.h +++ b/include/tcg/startup.h @@ -45,6 +45,13 @@ void tcg_init(size_t tb_size, int splitwx, unsigned max_cpus); */ void tcg_register_thread(void); +/** + * tcg_unregister_thread: Unregister this thread with the TCG runtime + * + * TBD + */ +void tcg_unregister_thread(void); + /** * tcg_prologue_init(): Generate the code for the TCG prologue * diff --git a/tcg/tcg.c b/tcg/tcg.c index 34e3056380..e5bbe8dc07 100644 --- a/tcg/tcg.c +++ b/tcg/tcg.c @@ -761,6 +761,15 @@ QEMU_BUILD_BUG_ON((int)(offsetof(CPUNegativeOffsetState, tlb.f[0]) - < MIN_TLB_MASK_TABLE_OFS); #endif +/* TODO: vCPU Hotplug: Need to come back and fix the TCG */ +static void free_tcg_plugin_context(TCGContext *s) +{ +#ifdef CONFIG_PLUGIN + g_ptr_array_unref(s->plugin_tb->insns); + g_free(s->plugin_tb); +#endif +} + /* * All TCG threads except the parent (i.e. the one that called tcg_context_init * and registered the target's TCG globals) must register with this function @@ -810,6 +819,21 @@ void tcg_register_thread(void) tcg_ctx = s; } + +void tcg_unregister_thread(void) +{ + TCGContext *s = tcg_ctx; + unsigned int n; + + /* Unclaim an entry in tcg_ctxs */ + n = qatomic_fetch_dec(&tcg_cur_ctxs); + g_assert(n > 1); + qatomic_store_release(&tcg_ctxs[n - 1], 0); + + free_tcg_plugin_context(s); + + g_free(s); +} #endif /* !CONFIG_USER_ONLY */ /* pool based memory allocation */ -- 2.34.1
