tcg: Add --accel tcg,split-wx property

Plumb the value through to alloc_code_gen_buffer.  This is not
supported by any os or tcg backend, so for now enabling it will
result in an error.

Reviewed-by: Joelle van Dyne <j@getutm.app>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/tcg-all.c

@@ -38,6 +38,7 @@ struct TCGState {
     AccelState parent_obj;
 
     bool mttcg_enabled;
+    int splitwx_enabled;
     unsigned long tb_size;
 };
 typedef struct TCGState TCGState;
@@ -94,6 +95,13 @@ static void tcg_accel_instance_init(Object *obj)
     TCGState *s = TCG_STATE(obj);
 
     s->mttcg_enabled = default_mttcg_enabled();
+
+    /* If debugging enabled, default "auto on", otherwise off. */
+#ifdef CONFIG_DEBUG_TCG
+    s->splitwx_enabled = -1;
+#else
+    s->splitwx_enabled = 0;
+#endif
 }
 
 bool mttcg_enabled;
@@ -102,7 +110,7 @@ static int tcg_init(MachineState *ms)
 {
     TCGState *s = TCG_STATE(current_accel());
 
-    tcg_exec_init(s->tb_size * 1024 * 1024);
+    tcg_exec_init(s->tb_size * 1024 * 1024, s->splitwx_enabled);
     mttcg_enabled = s->mttcg_enabled;
 
     /*
@@ -179,6 +187,18 @@ static void tcg_set_tb_size(Object *obj, Visitor *v,
     s->tb_size = value;
 }
 
+static bool tcg_get_splitwx(Object *obj, Error **errp)
+{
+    TCGState *s = TCG_STATE(obj);
+    return s->splitwx_enabled;
+}
+
+static void tcg_set_splitwx(Object *obj, bool value, Error **errp)
+{
+    TCGState *s = TCG_STATE(obj);
+    s->splitwx_enabled = value;
+}
+
 static void tcg_accel_class_init(ObjectClass *oc, void *data)
 {
     AccelClass *ac = ACCEL_CLASS(oc);
@@ -196,6 +216,10 @@ static void tcg_accel_class_init(ObjectClass *oc, void *data)
     object_class_property_set_description(oc, "tb-size",
         "TCG translation block cache size");
 
+    object_class_property_add_bool(oc, "split-wx",
+        tcg_get_splitwx, tcg_set_splitwx);
+    object_class_property_set_description(oc, "split-wx",
+        "Map jit pages into separate RW and RX regions");
 }
 
 static const TypeInfo tcg_accel_type = {

accel/tcg/translate-all.c

@@ -1015,13 +1015,19 @@ static inline void *split_cross_256mb(void *buf1, size_t size1)
 static uint8_t static_code_gen_buffer[DEFAULT_CODE_GEN_BUFFER_SIZE]
     __attribute__((aligned(CODE_GEN_ALIGN)));
 
-static bool alloc_code_gen_buffer(size_t tb_size, Error **errp)
+static bool alloc_code_gen_buffer(size_t tb_size, int splitwx, Error **errp)
 {
-    void *buf = static_code_gen_buffer;
+    void *buf, *end;
-    void *end = static_code_gen_buffer + sizeof(static_code_gen_buffer);
     size_t size;
 
+    if (splitwx > 0) {
+        error_setg(errp, "jit split-wx not supported");
+        return false;
+    }
+
     /* page-align the beginning and end of the buffer */
+    buf = static_code_gen_buffer;
+    end = static_code_gen_buffer + sizeof(static_code_gen_buffer);
     buf = QEMU_ALIGN_PTR_UP(buf, qemu_real_host_page_size);
     end = QEMU_ALIGN_PTR_DOWN(end, qemu_real_host_page_size);
 
@@ -1050,9 +1056,16 @@ static bool alloc_code_gen_buffer(size_t tb_size, Error **errp)
     return true;
 }
 #elif defined(_WIN32)
-static bool alloc_code_gen_buffer(size_t size, Error **errp)
+static bool alloc_code_gen_buffer(size_t size, int splitwx, Error **errp)
 {
-    void *buf = VirtualAlloc(NULL, size, MEM_RESERVE | MEM_COMMIT,
+    void *buf;
+
+    if (splitwx > 0) {
+        error_setg(errp, "jit split-wx not supported");
+        return false;
+    }
+
+    buf = VirtualAlloc(NULL, size, MEM_RESERVE | MEM_COMMIT,
                              PAGE_EXECUTE_READWRITE);
     if (buf == NULL) {
         error_setg_win32(errp, GetLastError(),
@@ -1065,12 +1078,17 @@ static bool alloc_code_gen_buffer(size_t size, Error **errp)
     return true;
 }
 #else
-static bool alloc_code_gen_buffer(size_t size, Error **errp)
+static bool alloc_code_gen_buffer(size_t size, int splitwx, Error **errp)
 {
     int prot = PROT_WRITE | PROT_READ | PROT_EXEC;
     int flags = MAP_PRIVATE | MAP_ANONYMOUS;
     void *buf;
 
+    if (splitwx > 0) {
+        error_setg(errp, "jit split-wx not supported");
+        return false;
+    }
+
     buf = mmap(NULL, size, prot, flags, -1, 0);
     if (buf == MAP_FAILED) {
         error_setg_errno(errp, errno,
@@ -1145,7 +1163,7 @@ static void tb_htable_init(void)
 /* Must be called before using the QEMU cpus. 'tb_size' is the size
    (in bytes) allocated to the translation buffer. Zero means default
    size. */
-void tcg_exec_init(unsigned long tb_size)
+void tcg_exec_init(unsigned long tb_size, int splitwx)
 {
     bool ok;
 
@@ -1154,7 +1172,8 @@ void tcg_exec_init(unsigned long tb_size)
     page_init();
     tb_htable_init();
 
-    ok = alloc_code_gen_buffer(size_code_gen_buffer(tb_size), &error_fatal);
+    ok = alloc_code_gen_buffer(size_code_gen_buffer(tb_size),
+                               splitwx, &error_fatal);
     assert(ok);
 
 #if defined(CONFIG_SOFTMMU)

bsd-user/main.c

@@ -909,7 +909,7 @@ int main(int argc, char **argv)
     }
 
     /* init tcg before creating CPUs and to get qemu_host_page_size */
-    tcg_exec_init(0);
+    tcg_exec_init(0, false);
 
     cpu_type = parse_cpu_option(cpu_model);
     cpu = cpu_create(cpu_type);

include/sysemu/tcg.h

@@ -8,7 +8,8 @@
 #ifndef SYSEMU_TCG_H
 #define SYSEMU_TCG_H
 
-void tcg_exec_init(unsigned long tb_size);
+void tcg_exec_init(unsigned long tb_size, int splitwx);
+
 #ifdef CONFIG_TCG
 extern bool tcg_allowed;
 #define tcg_enabled() (tcg_allowed)

linux-user/main.c

@@ -701,7 +701,7 @@ int main(int argc, char **argv, char **envp)
     cpu_type = parse_cpu_option(cpu_model);
 
     /* init tcg before creating CPUs and to get qemu_host_page_size */
-    tcg_exec_init(0);
+    tcg_exec_init(0, false);
 
     cpu = cpu_create(cpu_type);
     env = cpu->env_ptr;

qemu-options.hx

@@ -115,6 +115,7 @@ DEF("accel", HAS_ARG, QEMU_OPTION_accel,
     "                igd-passthru=on|off (enable Xen integrated Intel graphics passthrough, default=off)\n"
     "                kernel-irqchip=on|off|split controls accelerated irqchip support (default=on)\n"
     "                kvm-shadow-mem=size of KVM shadow MMU in bytes\n"
+    "                split-wx=on|off (enable TCG split w^x mapping)\n"
     "                tb-size=n (TCG translation block cache size)\n"
     "                thread=single|multi (enable multi-threaded TCG)\n", QEMU_ARCH_ALL)
 SRST
@@ -140,6 +141,12 @@ SRST
     ``kvm-shadow-mem=size``
         Defines the size of the KVM shadow MMU.
 
+    ``split-wx=on|off``
+        Controls the use of split w^x mapping for the TCG code generation
+        buffer. Some operating systems require this to be enabled, and in
+        such a case this will default on. On other operating systems, this
+        will default off, but one may enable this for testing or debugging.
+
     ``tb-size=n``
         Controls the size (in MiB) of the TCG translation block cache.
 

tcg/aarch64/tcg-target.h

@@ -155,5 +155,6 @@ void tb_target_set_jmp_target(uintptr_t, uintptr_t, uintptr_t, uintptr_t);
 #define TCG_TARGET_NEED_LDST_LABELS
 #endif
 #define TCG_TARGET_NEED_POOL_LABELS
+#define TCG_TARGET_SUPPORT_MIRROR       0
 
 #endif /* AARCH64_TCG_TARGET_H */

tcg/arm/tcg-target.h

@@ -142,5 +142,6 @@ void tb_target_set_jmp_target(uintptr_t, uintptr_t, uintptr_t, uintptr_t);
 #define TCG_TARGET_NEED_LDST_LABELS
 #endif
 #define TCG_TARGET_NEED_POOL_LABELS
+#define TCG_TARGET_SUPPORT_MIRROR       0
 
 #endif

tcg/i386/tcg-target.h

@@ -235,5 +235,6 @@ static inline void tb_target_set_jmp_target(uintptr_t tc_ptr, uintptr_t jmp_rx,
 #define TCG_TARGET_NEED_LDST_LABELS
 #endif
 #define TCG_TARGET_NEED_POOL_LABELS
+#define TCG_TARGET_SUPPORT_MIRROR       0
 
 #endif

tcg/mips/tcg-target.h

@@ -201,6 +201,7 @@ extern bool use_mips32r2_instructions;
 
 #define TCG_TARGET_DEFAULT_MO (0)
 #define TCG_TARGET_HAS_MEMORY_BSWAP     1
+#define TCG_TARGET_SUPPORT_MIRROR       0
 
 void tb_target_set_jmp_target(uintptr_t, uintptr_t, uintptr_t, uintptr_t);
 

tcg/ppc/tcg-target.h

@@ -185,5 +185,6 @@ void tb_target_set_jmp_target(uintptr_t, uintptr_t, uintptr_t, uintptr_t);
 #define TCG_TARGET_NEED_LDST_LABELS
 #endif
 #define TCG_TARGET_NEED_POOL_LABELS
+#define TCG_TARGET_SUPPORT_MIRROR       0
 
 #endif

tcg/riscv/tcg-target.h

@@ -171,5 +171,6 @@ void tb_target_set_jmp_target(uintptr_t, uintptr_t, uintptr_t, uintptr_t);
 #define TCG_TARGET_NEED_POOL_LABELS
 
 #define TCG_TARGET_HAS_MEMORY_BSWAP 0
+#define TCG_TARGET_SUPPORT_MIRROR   0
 
 #endif

tcg/s390/tcg-target.h

@@ -159,5 +159,6 @@ static inline void tb_target_set_jmp_target(uintptr_t tc_ptr, uintptr_t jmp_rx,
 #define TCG_TARGET_NEED_LDST_LABELS
 #endif
 #define TCG_TARGET_NEED_POOL_LABELS
+#define TCG_TARGET_SUPPORT_MIRROR       0
 
 #endif

tcg/sparc/tcg-target.h

@@ -172,5 +172,6 @@ extern bool use_vis3_instructions;
 void tb_target_set_jmp_target(uintptr_t, uintptr_t, uintptr_t, uintptr_t);
 
 #define TCG_TARGET_NEED_POOL_LABELS
+#define TCG_TARGET_SUPPORT_MIRROR       0
 
 #endif

tcg/tci/tcg-target.h

@@ -198,6 +198,7 @@ void tci_disas(uint8_t opc);
 #define TCG_TARGET_DEFAULT_MO  (0)
 
 #define TCG_TARGET_HAS_MEMORY_BSWAP     1
+#define TCG_TARGET_SUPPORT_MIRROR       0
 
 static inline void tb_target_set_jmp_target(uintptr_t tc_ptr, uintptr_t jmp_rx,
                                             uintptr_t jmp_rw, uintptr_t addr)