Re: [PATCH v7 14/18] cpu: Call plugin hooks only when ready

[Akihiko Odaki]

On 2023/09/12 17:46, Philippe Mathieu-Daudé wrote:

Hi Akihiko,

On 12/9/23 09:12, Akihiko Odaki wrote:

The initialization and exit hooks will not affect the state of vCPU,


What about:

  qemu_plugin_vcpu_init_hook()
    -> plugin_cpu_update__locked()
   -> plugin_cpu_update__async()
  -> bitmap_copy(cpu->plugin_mask, ...)
     tcg_flush_jmp_cache(cpu)
     -> qatomic_set(>tb_jmp_cache->array[i].tb, ...)

?


Hi,

bitmap_copy(cpu->plugin_mask, ...) is contained in the plugin 
infrastructure and shouldn't matter.


The TCG is not started filling caches so tcg_flush_jmp_cache() is 
effectively nop though that is not clearly stated.


By the way, I found plugin_cpu_update__locked() will not synchronously 
call plugin_cpu_update__async() after this change because cpu->created 
will be always true for the system emulation. For user space emulation, 
it has already been broken and it *always* synchronously calls the 
function since cpu->created is not set.


I wrote a change to replace cpu->created with DEVICE(cpu)->realized and 
added to the base patch series ("[PATCH v3 03/12] plugins: Check if vCPU 
is realized" in "[PATCH v3 00/12] gdbstub and TCG plugin improvements").


Regards,
Akihiko Odaki

Re: [PATCH v7 14/18] cpu: Call plugin hooks only when ready

[Philippe Mathieu-Daudé]

Hi Akihiko,

On 12/9/23 09:12, Akihiko Odaki wrote:

The initialization and exit hooks will not affect the state of vCPU,


What about:

 qemu_plugin_vcpu_init_hook()
   -> plugin_cpu_update__locked()
  -> plugin_cpu_update__async()
 -> bitmap_copy(cpu->plugin_mask, ...)
tcg_flush_jmp_cache(cpu)
-> qatomic_set(>tb_jmp_cache->array[i].tb, ...)

?


but they may depend on the state of vCPU. Therefore, it's better to
call plugin hooks after the vCPU state is fully initialized and before
it gets uninitialized.

Signed-off-by: Akihiko Odaki 
---
  cpu.c| 11 ---
  hw/core/cpu-common.c | 10 ++
  2 files changed, 10 insertions(+), 11 deletions(-)

[PATCH v7 14/18] cpu: Call plugin hooks only when ready

[Akihiko Odaki]

The initialization and exit hooks will not affect the state of vCPU,
but they may depend on the state of vCPU. Therefore, it's better to
call plugin hooks after the vCPU state is fully initialized and before
it gets uninitialized.

Signed-off-by: Akihiko Odaki 
---
 cpu.c| 11 ---
 hw/core/cpu-common.c | 10 ++
 2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/cpu.c b/cpu.c
index 1c948d1161..2552c85249 100644
--- a/cpu.c
+++ b/cpu.c
@@ -42,7 +42,6 @@
 #include "hw/core/accel-cpu.h"
 #include "trace/trace-root.h"
 #include "qemu/accel.h"
-#include "qemu/plugin.h"
 
 uintptr_t qemu_host_page_size;
 intptr_t qemu_host_page_mask;
@@ -148,11 +147,6 @@ void cpu_exec_realizefn(CPUState *cpu, Error **errp)
 /* Wait until cpu initialization complete before exposing cpu. */
 cpu_list_add(cpu);
 
-/* Plugin initialization must wait until cpu_index assigned. */
-if (tcg_enabled()) {
-qemu_plugin_vcpu_init_hook(cpu);
-}
-
 #ifdef CONFIG_USER_ONLY
 assert(qdev_get_vmsd(DEVICE(cpu)) == NULL ||
qdev_get_vmsd(DEVICE(cpu))->unmigratable);
@@ -179,11 +173,6 @@ void cpu_exec_unrealizefn(CPUState *cpu)
 }
 #endif
 
-/* Call the plugin hook before clearing cpu->cpu_index in cpu_list_remove 
*/
-if (tcg_enabled()) {
-qemu_plugin_vcpu_exit_hook(cpu);
-}
-
 cpu_list_remove(cpu);
 /*
  * Now that the vCPU has been removed from the RCU list, we can call
diff --git a/hw/core/cpu-common.c b/hw/core/cpu-common.c
index ced66c2b34..be1544687e 100644
--- a/hw/core/cpu-common.c
+++ b/hw/core/cpu-common.c
@@ -209,6 +209,11 @@ static void cpu_common_realizefn(DeviceState *dev, Error 
**errp)
 cpu_resume(cpu);
 }
 
+/* Plugin initialization must wait until the cpu is fully realized. */
+if (tcg_enabled()) {
+qemu_plugin_vcpu_init_hook(cpu);
+}
+
 /* NOTE: latest generic point where the cpu is fully realized */
 }
 
@@ -216,6 +221,11 @@ static void cpu_common_unrealizefn(DeviceState *dev)
 {
 CPUState *cpu = CPU(dev);
 
+/* Call the plugin hook before clearing the cpu is fully unrealized */
+if (tcg_enabled()) {
+qemu_plugin_vcpu_exit_hook(cpu);
+}
+
 /* NOTE: latest generic point before the cpu is fully unrealized */
 cpu_exec_unrealizefn(cpu);
 }
-- 
2.42.0