[Qemu-devel] [patch v4 09/16] memory: introduce mmio request pending to anti nested DMA

[Liu Ping Fan <pingfank@linux.vnet.ibm.com>]

Rejecting the nested mmio request which does not aim at RAM, so we
can avoid the potential deadlock caused by the random lock sequence
of two device's local lock.

Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
---
 cpus.c              |   14 ++++++++++++++
 exec.c              |   50 ++++++++++++++++++++++++++++++++++++--------------
 hw/hw.h             |    1 +
 kvm-all.c           |    2 ++
 qemu-thread-posix.h |    3 +++
 qemu-thread.h       |    2 ++
 6 files changed, 58 insertions(+), 14 deletions(-)

diff --git a/cpus.c b/cpus.c
index 4cd7f85..365a512 100644
--- a/cpus.c
+++ b/cpus.c
@@ -729,6 +729,18 @@ static void qemu_kvm_wait_io_event(CPUArchState *env)
     qemu_wait_io_event_common(env);
 }
 
+int get_context_type(void)
+{
+    QemuThread *t = pthread_getspecific(qemu_thread_key);
+    return t->context_type;
+}
+
+void set_context_type(int type)
+{
+    QemuThread *t = pthread_getspecific(qemu_thread_key);
+    t->context_type = type;
+}
+
 static void *qemu_kvm_cpu_thread_fn(void *arg)
 {
     CPUArchState *env = arg;
@@ -736,6 +748,8 @@ static void *qemu_kvm_cpu_thread_fn(void *arg)
     int r;
 
     pthread_setspecific(qemu_thread_key, cpu->thread);
+    set_context_type(0);
+
     qemu_mutex_lock(&qemu_global_mutex);
     qemu_thread_get_self(cpu->thread);
     env->thread_id = qemu_get_thread_id();
diff --git a/exec.c b/exec.c
index 91b859b..a0327a1 100644
--- a/exec.c
+++ b/exec.c
@@ -3490,7 +3490,9 @@ void cpu_physical_memory_rw(target_phys_addr_t addr, uint8_t *buf,
     uint32_t val;
     target_phys_addr_t page;
     MemoryRegionSection *section, obj_mrs;
-    int safe_ref;
+    int safe_ref, nested_dma = 0;
+    QemuThread *thread = pthread_getspecific(qemu_thread_key);
+    int context = thread->context_type;
 
     while (len > 0) {
         page = addr & TARGET_PAGE_MASK;
@@ -3500,7 +3502,8 @@ void cpu_physical_memory_rw(target_phys_addr_t addr, uint8_t *buf,
         qemu_mutex_lock(&mem_map_lock);
         safe_ref = phys_page_lookup(page, &obj_mrs);
         qemu_mutex_unlock(&mem_map_lock);
-        if (safe_ref == 0) {
+
+        if (safe_ref == 0 && context == 1) {
             qemu_mutex_lock_iothread();
             qemu_mutex_lock(&mem_map_lock);
             /* At the 2nd try, mem map can change, so need to judge it again */
@@ -3511,7 +3514,9 @@ void cpu_physical_memory_rw(target_phys_addr_t addr, uint8_t *buf,
             }
         }
         section = &obj_mrs;
-
+        if (context == 1) {
+            nested_dma = thread->mmio_request_pending++ > 1 ? 1 : 0;
+        }
         if (is_write) {
             if (!memory_region_is_ram(section->mr)) {
                 target_phys_addr_t addr1;
@@ -3521,17 +3526,23 @@ void cpu_physical_memory_rw(target_phys_addr_t addr, uint8_t *buf,
                 if (l >= 4 && ((addr1 & 3) == 0)) {
                     /* 32 bit write access */
                     val = ldl_p(buf);
-                    io_mem_write(section->mr, addr1, val, 4);
+                    if (!nested_dma) {
+                        io_mem_write(section->mr, addr1, val, 4);
+                    }
                     l = 4;
                 } else if (l >= 2 && ((addr1 & 1) == 0)) {
                     /* 16 bit write access */
                     val = lduw_p(buf);
-                    io_mem_write(section->mr, addr1, val, 2);
+                    if (!nested_dma) {
+                        io_mem_write(section->mr, addr1, val, 2);
+                    }
                     l = 2;
                 } else {
                     /* 8 bit write access */
                     val = ldub_p(buf);
-                    io_mem_write(section->mr, addr1, val, 1);
+                    if (!nested_dma) {
+                        io_mem_write(section->mr, addr1, val, 1);
+                    }
                     l = 1;
                 }
             } else if (!section->readonly) {
@@ -3552,24 +3563,31 @@ void cpu_physical_memory_rw(target_phys_addr_t addr, uint8_t *buf,
             }
         } else {
             if (!(memory_region_is_ram(section->mr) ||
-                  memory_region_is_romd(section->mr))) {
+                  memory_region_is_romd(section->mr)) &&
+                    !nested_dma) {
                 target_phys_addr_t addr1;
                 /* I/O case */
                 addr1 = memory_region_section_addr(section, addr);
                 if (l >= 4 && ((addr1 & 3) == 0)) {
                     /* 32 bit read access */
-                    val = io_mem_read(section->mr, addr1, 4);
-                    stl_p(buf, val);
+                    if (!nested_dma) {
+                        val = io_mem_read(section->mr, addr1, 4);
+                        stl_p(buf, val);
+                    }
                     l = 4;
                 } else if (l >= 2 && ((addr1 & 1) == 0)) {
                     /* 16 bit read access */
-                    val = io_mem_read(section->mr, addr1, 2);
-                    stw_p(buf, val);
+                    if (!nested_dma) {
+                        val = io_mem_read(section->mr, addr1, 2);
+                        stw_p(buf, val);
+                    }
                     l = 2;
                 } else {
                     /* 8 bit read access */
-                    val = io_mem_read(section->mr, addr1, 1);
-                    stb_p(buf, val);
+                    if (!nested_dma) {
+                        val = io_mem_read(section->mr, addr1, 1);
+                        stb_p(buf, val);
+                    }
                     l = 1;
                 }
             } else {
@@ -3586,7 +3604,11 @@ void cpu_physical_memory_rw(target_phys_addr_t addr, uint8_t *buf,
         len -= l;
         buf += l;
         addr += l;
-        if (safe_ref == 0) {
+
+        if (context == 1) {
+            thread->mmio_request_pending--;
+        }
+        if (safe_ref == 0 && context == 1) {
             qemu_mutex_unlock_iothread();
         }
     }
diff --git a/hw/hw.h b/hw/hw.h
index e5cb9bf..935b045 100644
--- a/hw/hw.h
+++ b/hw/hw.h
@@ -12,6 +12,7 @@
 #include "irq.h"
 #include "qemu-file.h"
 #include "vmstate.h"
+#include "qemu-thread.h"
 
 #ifdef NEED_CPU_H
 #if TARGET_LONG_BITS == 64
diff --git a/kvm-all.c b/kvm-all.c
index 34b02c1..b3fa597 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -1562,10 +1562,12 @@ int kvm_cpu_exec(CPUArchState *env)
             break;
         case KVM_EXIT_MMIO:
             DPRINTF("handle_mmio\n");
+            set_context_type(1);
             cpu_physical_memory_rw(run->mmio.phys_addr,
                                    run->mmio.data,
                                    run->mmio.len,
                                    run->mmio.is_write);
+            set_context_type(0);
             ret = 0;
             break;
         case KVM_EXIT_IRQ_WINDOW_OPEN:
diff --git a/qemu-thread-posix.h b/qemu-thread-posix.h
index 2607b1c..9fcc6f8 100644
--- a/qemu-thread-posix.h
+++ b/qemu-thread-posix.h
@@ -12,6 +12,9 @@ struct QemuCond {
 
 struct QemuThread {
     pthread_t thread;
+    /* 0 clean; 1 mmio; 2 io */
+    int context_type;
+    int mmio_request_pending;
 };
 
 extern pthread_key_t qemu_thread_key;
diff --git a/qemu-thread.h b/qemu-thread.h
index 4a6427d..88eaf94 100644
--- a/qemu-thread.h
+++ b/qemu-thread.h
@@ -45,6 +45,8 @@ void *qemu_thread_join(QemuThread *thread);
 void qemu_thread_get_self(QemuThread *thread);
 bool qemu_thread_is_self(QemuThread *thread);
 void qemu_thread_exit(void *retval);
+int get_context_type(void);
+void set_context_type(int type);
 
 void qemu_thread_key_create(void);
 #endif
-- 
1.7.4.4