[Qemu-devel] [PATCH 2/2] trace: separate MMIO tracepoints from TB-access tracepoints

[Hollis Blanchard]

Memory accesses to code which has previously been translated into a TB show up
in the MMIO path, so that they may invalidate the TB. It's extremely confusing
to mix those in with device MMIOs, so split them into their own tracepoint.

Signed-off-by: Hollis Blanchard <address@hidden>

---
It took many hours to figure out why some RAM accesses were coming through the
MMIO path instead of being handled inline in the TBs.

On IRC, Paolo expressed some concern about performance, but ultimately agreed
that adding one conditional to an already heavy codepath wouldn't have much
impact.
---
 memory.c     | 25 +++++++++++++++++++++++++
 trace-events |  2 ++
 2 files changed, 27 insertions(+)

diff --git a/memory.c b/memory.c
index 6ae7bae..3d125c9 100644
--- a/memory.c
+++ b/memory.c
@@ -403,6 +403,11 @@ static MemTxResult 
memory_region_oldmmio_read_accessor(MemoryRegion *mr,
     tmp = mr->ops->old_mmio.read[ctz32(size)](mr->opaque, addr);
     if (mr->subpage) {
         trace_memory_region_subpage_read(cpu_index, mr, addr, tmp, size);
+    } else if (mr == &io_mem_notdirty) {
+        /* Accesses to code which has previously been translated into a TB show
+         * up in the MMIO path, as accesses to the io_mem_notdirty
+         * MemoryRegion. */
+        trace_memory_region_ops_tb_read(cpu_index, addr, tmp, size);
     } else if (TRACE_MEMORY_REGION_OPS_READ_ENABLED) {
         hwaddr abs_addr = memory_region_to_absolute_addr(mr, addr);
         trace_memory_region_ops_read(cpu_index, mr, abs_addr, tmp, size);
@@ -428,6 +433,11 @@ static MemTxResult  
memory_region_read_accessor(MemoryRegion *mr,
     tmp = mr->ops->read(mr->opaque, addr, size);
     if (mr->subpage) {
         trace_memory_region_subpage_read(cpu_index, mr, addr, tmp, size);
+    } else if (mr == &io_mem_notdirty) {
+        /* Accesses to code which has previously been translated into a TB show
+         * up in the MMIO path, as accesses to the io_mem_notdirty
+         * MemoryRegion. */
+        trace_memory_region_ops_tb_read(cpu_index, addr, tmp, size);
     } else if (TRACE_MEMORY_REGION_OPS_READ_ENABLED) {
         hwaddr abs_addr = memory_region_to_absolute_addr(mr, addr);
         trace_memory_region_ops_read(cpu_index, mr, abs_addr, tmp, size);
@@ -454,6 +464,11 @@ static MemTxResult 
memory_region_read_with_attrs_accessor(MemoryRegion *mr,
     r = mr->ops->read_with_attrs(mr->opaque, addr, &tmp, size, attrs);
     if (mr->subpage) {
         trace_memory_region_subpage_read(cpu_index, mr, addr, tmp, size);
+    } else if (mr == &io_mem_notdirty) {
+        /* Accesses to code which has previously been translated into a TB show
+         * up in the MMIO path, as accesses to the io_mem_notdirty
+         * MemoryRegion. */
+        trace_memory_region_ops_tb_read(cpu_index, addr, tmp, size);
     } else if (TRACE_MEMORY_REGION_OPS_READ_ENABLED) {
         hwaddr abs_addr = memory_region_to_absolute_addr(mr, addr);
         trace_memory_region_ops_read(cpu_index, mr, abs_addr, tmp, size);
@@ -479,6 +494,11 @@ static MemTxResult 
memory_region_oldmmio_write_accessor(MemoryRegion *mr,
     tmp = (*value >> shift) & mask;
     if (mr->subpage) {
         trace_memory_region_subpage_write(cpu_index, mr, addr, tmp, size);
+    } else if (mr == &io_mem_notdirty) {
+        /* Accesses to code which has previously been translated into a TB show
+         * up in the MMIO path, as accesses to the io_mem_notdirty
+         * MemoryRegion. */
+        trace_memory_region_ops_tb_write(cpu_index, addr, tmp, size);
     } else if (TRACE_MEMORY_REGION_OPS_WRITE_ENABLED) {
         hwaddr abs_addr = memory_region_to_absolute_addr(mr, addr);
         trace_memory_region_ops_write(cpu_index, mr, abs_addr, tmp, size);
@@ -504,6 +524,11 @@ static MemTxResult 
memory_region_write_accessor(MemoryRegion *mr,
     tmp = (*value >> shift) & mask;
     if (mr->subpage) {
         trace_memory_region_subpage_write(cpu_index, mr, addr, tmp, size);
+    } else if (mr == &io_mem_notdirty) {
+        /* Accesses to code which has previously been translated into a TB show
+         * up in the MMIO path, as accesses to the io_mem_notdirty
+         * MemoryRegion. */
+        trace_memory_region_ops_tb_write(cpu_index, addr, tmp, size);
     } else if (TRACE_MEMORY_REGION_OPS_WRITE_ENABLED) {
         hwaddr abs_addr = memory_region_to_absolute_addr(mr, addr);
         trace_memory_region_ops_write(cpu_index, mr, abs_addr, tmp, size);
diff --git a/trace-events b/trace-events
index 756ce86..7994420 100644
--- a/trace-events
+++ b/trace-events
@@ -1630,6 +1630,8 @@ memory_region_ops_read(int cpu_index, void *mr, uint64_t 
addr, uint64_t value, u
 memory_region_ops_write(int cpu_index, void *mr, uint64_t addr, uint64_t 
value, unsigned size) "cpu %d mr %p addr %#"PRIx64" value %#"PRIx64" size %u"
 memory_region_subpage_read(int cpu_index, void *mr, uint64_t offset, uint64_t 
value, unsigned size) "cpu %d mr %p offset %#"PRIx64" value %#"PRIx64" size %u"
 memory_region_subpage_write(int cpu_index, void *mr, uint64_t offset, uint64_t 
value, unsigned size) "cpu %d mr %p offset %#"PRIx64" value %#"PRIx64" size %u"
+memory_region_ops_tb_read(int cpu_index, uint64_t addr, uint64_t value, 
unsigned size) "cpu %d addr %#"PRIx64" value %#"PRIx64" size %u"
+memory_region_ops_tb_write(int cpu_index, uint64_t addr, uint64_t value, 
unsigned size) "cpu %d addr %#"PRIx64" value %#"PRIx64" size %u"
 
 # qom/object.c
 object_dynamic_cast_assert(const char *type, const char *target, const char 
*file, int line, const char *func) "%s->%s (%s:%d:%s)"
-- 
1.9.1