[PATCH 1/5] hw/cpu: Extend CPUState::cluster_index documentation

[Philippe Mathieu-Daudé]

Copy part of the description of commit f7b78602fd ("accel/tcg:
Add cluster number to TCG TB hash") in tcg_cpu_init_cflags(),
improving a bit CPUState::cluster_index documentation.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 accel/tcg/tcg-accel-ops.c | 13 ++++++++++++-
 include/hw/core/cpu.h     |  2 ++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/accel/tcg/tcg-accel-ops.c b/accel/tcg/tcg-accel-ops.c
index 19cbf1db3a..654aeec04c 100644
--- a/accel/tcg/tcg-accel-ops.c
+++ b/accel/tcg/tcg-accel-ops.c
@@ -44,7 +44,18 @@
 
 void tcg_cpu_init_cflags(CPUState *cpu, bool parallel)
 {
-    uint32_t cflags = cpu->cluster_index << CF_CLUSTER_SHIFT;
+    uint32_t cflags;
+
+    /*
+     * Include the cluster number in the hash we use to look up TBs.
+     * This is important because a TB that is valid for one cluster at
+     * a given physical address and set of CPU flags is not necessarily
+     * valid for another:
+     * the two clusters may have different views of physical memory, or
+     * may have different CPU features (eg FPU present or absent).
+     */
+    cflags = cpu->cluster_index << CF_CLUSTER_SHIFT;
+
     cflags |= parallel ? CF_PARALLEL : 0;
     cflags |= icount_enabled() ? CF_USE_ICOUNT : 0;
     cpu->tcg_cflags = cflags;
diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
index 2417597236..d427db0bc7 100644
--- a/include/hw/core/cpu.h
+++ b/include/hw/core/cpu.h
@@ -272,6 +272,8 @@ struct qemu_work_item;
  *   to a cluster this will be UNASSIGNED_CLUSTER_INDEX; otherwise it will
  *   be the same as the cluster-id property of the CPU object's 
TYPE_CPU_CLUSTER
  *   QOM parent.
+ *   Under TCG this value is propagated to @tcg_cflags.
+ *   See TranslationBlock::TCG CF_CLUSTER_MASK.
  * @tcg_cflags: Pre-computed cflags for this cpu.
  * @nr_cores: Number of cores within this CPU package.
  * @nr_threads: Number of threads within this CPU.
-- 
2.38.1