[Qemu-devel] [PATCH 3/3] exec.c: Collect AddressSpace related fields into a CPUAddressSpace struct

[Peter Maydell <peter.maydell@linaro.org>]

Gather up all the fields currently in CPUState which deal with the CPU's
AddressSpace into a separate CPUAddressSpace struct. This paves the way
for allowing the CPU to know about more than one AddressSpace.

The rearrangement also allows us to make the MemoryListener a directly
embedded object in the CPUAddressSpace (it could not be embedded in
CPUState because 'struct MemoryListener' isn't defined for the user-only
builds). This allows us to resolve the FIXME in tcg_commit() by going
directly from the MemoryListener to the CPUAddressSpace.

This patch extracts the actual update of the cached dispatch pointer
from cpu_reload_memory_map() (which is renamed accordingly to
cpu_reloading_memory_map() as it is only responsible for breaking
cpu-exec.c's RCU critical section now). This lets us keep the definition
of the CPUAddressSpace struct private to exec.c.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 cpu-exec.c              | 13 +++---------
 exec.c                  | 56 +++++++++++++++++++++++++++++++++----------------
 include/exec/exec-all.h |  2 +-
 include/qemu/typedefs.h |  1 +
 include/qom/cpu.h       |  7 +++++--
 5 files changed, 48 insertions(+), 31 deletions(-)

diff --git a/cpu-exec.c b/cpu-exec.c
index d84c2cd..cdfb0de 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -145,10 +145,8 @@ void cpu_resume_from_signal(CPUState *cpu, void *puc)
     siglongjmp(cpu->jmp_env, 1);
 }
 
-void cpu_reload_memory_map(CPUState *cpu)
+void cpu_reloading_memory_map(void)
 {
-    AddressSpaceDispatch *d;
-
     if (qemu_in_vcpu_thread()) {
         /* The guest can in theory prolong the RCU critical section as long
          * as it feels like. The major problem with this is that because it
@@ -167,17 +165,12 @@ void cpu_reload_memory_map(CPUState *cpu)
          * part of this callback might become unnecessary.)
          *
          * This pair matches cpu_exec's rcu_read_lock()/rcu_read_unlock(), which
-         * only protects cpu->as->dispatch.  Since we reload it below, we can
-         * split the critical section.
+         * only protects cpuas->dispatch.  Since we know our caller is about
+         * to reload it, it's safe to split the critical section.
          */
         rcu_read_unlock();
         rcu_read_lock();
     }
-
-    /* The CPU and TLB are protected by the iothread lock.  */
-    d = atomic_rcu_read(&cpu->as->dispatch);
-    cpu->memory_dispatch = d;
-    tlb_flush(cpu, 1);
 }
 #endif
 
diff --git a/exec.c b/exec.c
index 2616394..ecefd18 100644
--- a/exec.c
+++ b/exec.c
@@ -158,6 +158,21 @@ static void memory_map_init(void);
 static void tcg_commit(MemoryListener *listener);
 
 static MemoryRegion io_mem_watch;
+
+/**
+ * CPUAddressSpace: all the information a CPU needs about an AddressSpace
+ * @cpu: the CPU whose AddressSpace this is
+ * @as: the AddressSpace itself
+ * @memory_dispatch: its dispatch pointer (cached, RCU protected)
+ * @tcg_as_listener: listener for tracking changes to the AddressSpace
+ */
+struct CPUAddressSpace {
+    CPUState *cpu;
+    AddressSpace *as;
+    struct AddressSpaceDispatch *memory_dispatch;
+    MemoryListener tcg_as_listener;
+};
+
 #endif
 
 #if !defined(CONFIG_USER_ONLY)
@@ -416,7 +431,7 @@ address_space_translate_for_iotlb(CPUState *cpu, hwaddr addr,
                                   hwaddr *xlat, hwaddr *plen)
 {
     MemoryRegionSection *section;
-    section = address_space_translate_internal(cpu->memory_dispatch,
+    section = address_space_translate_internal(cpu->cpu_ases[0].memory_dispatch,
                                                addr, xlat, plen, false);
 
     assert(!section->mr->iommu_ops);
@@ -503,13 +518,16 @@ void tcg_cpu_address_space_init(CPUState *cpu, AddressSpace *as)
     /* We only support one address space per cpu at the moment.  */
     assert(cpu->as == as);
 
-    if (cpu->tcg_as_listener) {
-        memory_listener_unregister(cpu->tcg_as_listener);
-    } else {
-        cpu->tcg_as_listener = g_new0(MemoryListener, 1);
+    if (cpu->cpu_ases) {
+        /* We've already registered the listener for our only AS */
+        return;
     }
-    cpu->tcg_as_listener->commit = tcg_commit;
-    memory_listener_register(cpu->tcg_as_listener, as);
+
+    cpu->cpu_ases = g_new0(CPUAddressSpace, 1);
+    cpu->cpu_ases[0].cpu = cpu;
+    cpu->cpu_ases[0].as = as;
+    cpu->cpu_ases[0].tcg_as_listener.commit = tcg_commit;
+    memory_listener_register(&cpu->cpu_ases[0].tcg_as_listener, as);
 }
 #endif
 
@@ -2097,7 +2115,8 @@ static uint16_t dummy_section(PhysPageMap *map, AddressSpace *as,
 
 MemoryRegion *iotlb_to_region(CPUState *cpu, hwaddr index)
 {
-    AddressSpaceDispatch *d = atomic_rcu_read(&cpu->memory_dispatch);
+    CPUAddressSpace *cpuas = &cpu->cpu_ases[0];
+    AddressSpaceDispatch *d = atomic_rcu_read(&cpuas->memory_dispatch);
     MemoryRegionSection *sections = d->map.sections;
 
     return sections[index & ~TARGET_PAGE_MASK].mr;
@@ -2156,19 +2175,20 @@ static void mem_commit(MemoryListener *listener)
 
 static void tcg_commit(MemoryListener *listener)
 {
-    CPUState *cpu;
+    CPUAddressSpace *cpuas;
+    AddressSpaceDispatch *d;
 
     /* since each CPU stores ram addresses in its TLB cache, we must
        reset the modified entries */
-    /* XXX: slow ! */
-    CPU_FOREACH(cpu) {
-        /* FIXME: Disentangle the cpu.h circular files deps so we can
-           directly get the right CPU from listener.  */
-        if (cpu->tcg_as_listener != listener) {
-            continue;
-        }
-        cpu_reload_memory_map(cpu);
-    }
+    cpuas = container_of(listener, CPUAddressSpace, tcg_as_listener);
+    cpu_reloading_memory_map();
+    /* The CPU and TLB are protected by the iothread lock.
+     * We reload the dispatch pointer now because cpu_reloading_memory_map()
+     * may have split the RCU critical section.
+     */
+    d = atomic_rcu_read(&cpuas->as->dispatch);
+    cpuas->memory_dispatch = d;
+    tlb_flush(cpuas->cpu, 1);
 }
 
 void address_space_init_dispatch(AddressSpace *as)
diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
index 2573e8c..53445a1 100644
--- a/include/exec/exec-all.h
+++ b/include/exec/exec-all.h
@@ -93,7 +93,7 @@ void QEMU_NORETURN cpu_loop_exit(CPUState *cpu);
 
 #if !defined(CONFIG_USER_ONLY)
 bool qemu_in_vcpu_thread(void);
-void cpu_reload_memory_map(CPUState *cpu);
+void cpu_reloading_memory_map(void);
 void tcg_cpu_address_space_init(CPUState *cpu, AddressSpace *as);
 /* cputlb.c */
 void tlb_flush_page(CPUState *cpu, target_ulong addr);
diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
index 6fdcbcd..df39eba 100644
--- a/include/qemu/typedefs.h
+++ b/include/qemu/typedefs.h
@@ -16,6 +16,7 @@ typedef struct BusClass BusClass;
 typedef struct BusState BusState;
 typedef struct CharDriverState CharDriverState;
 typedef struct CompatProperty CompatProperty;
+typedef struct CPUAddressSpace CPUAddressSpace;
 typedef struct DeviceState DeviceState;
 typedef struct DeviceListener DeviceListener;
 typedef struct DisplayChangeListener DisplayChangeListener;
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 39f0f19..ca18e49 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -228,6 +228,10 @@ struct kvm_run;
  * This allows a single read-compare-cbranch-write sequence to test
  * for both decrementer underflow and exceptions.
  * @can_do_io: Nonzero if memory-mapped IO is safe.
+ * @cpu_ases: Pointer to array of CPUAddressSpaces (which define the
+ *            AddressSpaces this CPU has)
+ * @as: Pointer to the first AddressSpace, for the convenience of targets which
+ *      only have a single AddressSpace
  * @env_ptr: Pointer to subclass-specific CPUArchState field.
  * @current_tb: Currently executing TB.
  * @gdb_regs: Additional GDB registers.
@@ -269,9 +273,8 @@ struct CPUState {
     int64_t icount_extra;
     sigjmp_buf jmp_env;
 
+    CPUAddressSpace *cpu_ases;
     AddressSpace *as;
-    struct AddressSpaceDispatch *memory_dispatch;
-    MemoryListener *tcg_as_listener;
 
     void *env_ptr; /* CPUArchState */
     struct TranslationBlock *current_tb;
-- 
1.9.1