[PATCH] spufs: allow SPU code to do syscalls

An SPU does not have a way to implement system calls
itself, but it can create intercepts to the kernel.

This patch uses the method defined by the JSRE interface
for C99 host library calls from an SPU to implement
Linux system calls. It uses the reserved SPU stop code
0x2104 for this, using the structure layout and syscall
numbers for ppc64-linux.

I'm still undecided wether it is better to have a list
of allowed syscalls or a list of forbidden syscalls,
since we can't allow an SPU to call all syscalls that
are defined for ppc64-linux.

This patch implements the easier choice of them, with a
blacklist that only prevents an SPU from calling anything
that interacts with its own execution, e.g fork, execve,
clone, vfork, exit, spu_run and spu_create and everything
that deals with signals.
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/cell/Makefile

@@ -6,5 +6,11 @@ obj-$(CONFIG_SPU_FS)	+= spu-base.o spufs/
 
 spu-base-y		+= spu_base.o spu_priv1.o
 
-builtin-spufs-$(CONFIG_SPU_FS)	+= spu_syscalls.o
-obj-y			+= $(builtin-spufs-m)
+# needed only when building loadable spufs.ko
+spufs-modular-$(CONFIG_SPU_FS) += spu_syscalls.o
+obj-y			+= $(spufs-modular-m)
+
+# always needed in kernel
+spufs-builtin-$(CONFIG_SPU_FS) += spu_callbacks.o
+obj-y			+= $(spufs-builtin-y) $(spufs-builtin-m)
+

arch/powerpc/platforms/cell/spufs/run.c

@@ -76,6 +76,90 @@ static inline int spu_reacquire_runnable(struct spu_context *ctx, u32 *npc,
 	return 0;
 }
 
+/*
+ * SPU syscall restarting is tricky because we violate the basic
+ * assumption that the signal handler is running on the interrupted
+ * thread. Here instead, the handler runs on PowerPC user space code,
+ * while the syscall was called from the SPU.
+ * This means we can only do a very rough approximation of POSIX
+ * signal semantics.
+ */
+int spu_handle_restartsys(struct spu_context *ctx, long *spu_ret,
+			  unsigned int *npc)
+{
+	int ret;
+
+	switch (*spu_ret) {
+	case -ERESTARTSYS:
+	case -ERESTARTNOINTR:
+		/*
+		 * Enter the regular syscall restarting for
+		 * sys_spu_run, then restart the SPU syscall
+		 * callback.
+		 */
+		*npc -= 8;
+		ret = -ERESTARTSYS;
+		break;
+	case -ERESTARTNOHAND:
+	case -ERESTART_RESTARTBLOCK:
+		/*
+		 * Restart block is too hard for now, just return -EINTR
+		 * to the SPU.
+		 * ERESTARTNOHAND comes from sys_pause, we also return
+		 * -EINTR from there.
+		 * Assume that we need to be restarted ourselves though.
+		 */
+		*spu_ret = -EINTR;
+		ret = -ERESTARTSYS;
+		break;
+	default:
+		printk(KERN_WARNING "%s: unexpected return code %ld\n",
+			__FUNCTION__, *spu_ret);
+		ret = 0;
+	}
+	return ret;
+}
+
+int spu_process_callback(struct spu_context *ctx)
+{
+	struct spu_syscall_block s;
+	u32 ls_pointer, npc;
+	char *ls;
+	long spu_ret;
+	int ret;
+
+	/* get syscall block from local store */
+	npc = ctx->ops->npc_read(ctx);
+	ls = ctx->ops->get_ls(ctx);
+	ls_pointer = *(u32*)(ls + npc);
+	if (ls_pointer > (LS_SIZE - sizeof(s)))
+		return -EFAULT;
+	memcpy(&s, ls + ls_pointer, sizeof (s));
+
+	/* do actual syscall without pinning the spu */
+	ret = 0;
+	spu_ret = -ENOSYS;
+	npc += 4;
+
+	if (s.nr_ret < __NR_syscalls) {
+		spu_release(ctx);
+		/* do actual system call from here */
+		spu_ret = spu_sys_callback(&s);
+		if (spu_ret <= -ERESTARTSYS) {
+			ret = spu_handle_restartsys(ctx, &spu_ret, &npc);
+		}
+		spu_acquire(ctx);
+		if (ret == -ERESTARTSYS)
+			return ret;
+	}
+
+	/* write result, jump over indirect pointer */
+	memcpy(ls + ls_pointer, &spu_ret, sizeof (spu_ret));
+	ctx->ops->npc_write(ctx, npc);
+	ctx->ops->runcntl_write(ctx, SPU_RUNCNTL_RUNNABLE);
+	return ret;
+}
+
 static inline int spu_process_events(struct spu_context *ctx)
 {
 	struct spu *spu = ctx->spu;
@@ -107,6 +191,13 @@ long spufs_run_spu(struct file *file, struct spu_context *ctx,
 		ret = spufs_wait(ctx->stop_wq, spu_stopped(ctx, status));
 		if (unlikely(ret))
 			break;
+		if ((*status & SPU_STATUS_STOPPED_BY_STOP) &&
+		    (*status >> SPU_STOP_STATUS_SHIFT == 0x2104)) {
+			ret = spu_process_callback(ctx);
+			if (ret)
+				break;
+			*status &= ~SPU_STATUS_STOPPED_BY_STOP;
+		}
 		if (unlikely(ctx->state != SPU_STATE_RUNNABLE)) {
 			ret = spu_reacquire_runnable(ctx, npc, status);
 			if (ret)

include/asm-powerpc/spu.h

@@ -149,6 +149,14 @@ int spu_irq_class_0_bottom(struct spu *spu);
 int spu_irq_class_1_bottom(struct spu *spu);
 void spu_irq_setaffinity(struct spu *spu, int cpu);
 
+/* system callbacks from the SPU */
+struct spu_syscall_block {
+	u64 nr_ret;
+	u64 parm[6];
+};
+extern long spu_sys_callback(struct spu_syscall_block *s);
+
+/* syscalls implemented in spufs */
 extern struct spufs_calls {
 	asmlinkage long (*create_thread)(const char __user *name,
 					unsigned int flags, mode_t mode);
@@ -399,7 +407,6 @@ struct spu_priv1 {
 #define SPU_GET_REVISION_BITS(vr)	(vr & SPU_REVISION_BITS)
 	u8  pad_0x28_0x100[0x100 - 0x28];			/* 0x28 */
 
-
 	/* Interrupt Area */
 	u64 int_mask_RW[3];					/* 0x100 */
 #define CLASS0_ENABLE_DMA_ALIGNMENT_INTR		0x1L