powerpc: Make load/store emulation use larger memory accesses

At the moment, emulation of loads and stores of up to 8 bytes to
unaligned addresses on a little-endian system uses a sequence of
single-byte loads or stores to memory.  This is rather inefficient,
and the code is hard to follow because it has many ifdefs.
In addition, the Power ISA has requirements on how unaligned accesses
are performed, which are not met by doing all accesses as
sequences of single-byte accesses.

Emulation of VSX loads and stores uses __copy_{to,from}_user,
which means the emulation code has no control on the size of
accesses.

To simplify this, we add new copy_mem_in() and copy_mem_out()
functions for accessing memory.  These use a sequence of the largest
possible aligned accesses, up to 8 bytes (or 4 on 32-bit systems),
to copy memory between a local buffer and user memory.  We then
rewrite {read,write}_mem_unaligned and the VSX load/store
emulation using these new functions.

These new functions also simplify the code in do_fp_load() and
do_fp_store() for the unaligned cases.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/lib/sstep.c

@@ -193,7 +193,6 @@ static nokprobe_inline unsigned long max_align(unsigned long x)
 	return x & -x;		/* isolates rightmost bit */
 }
 
-
 static nokprobe_inline unsigned long byterev_2(unsigned long x)
 {
 	return ((x >> 8) & 0xff) | ((x & 0xff) << 8);
@@ -239,56 +238,69 @@ static nokprobe_inline int read_mem_aligned(unsigned long *dest,
 	return err;
 }
 
-static nokprobe_inline int read_mem_unaligned(unsigned long *dest,
-				unsigned long ea, int nb, struct pt_regs *regs)
+/*
+ * Copy from userspace to a buffer, using the largest possible
+ * aligned accesses, up to sizeof(long).
+ */
+static int nokprobe_inline copy_mem_in(u8 *dest, unsigned long ea, int nb)
 {
-	int err;
-	unsigned long x, b, c;
-#ifdef __LITTLE_ENDIAN__
-	int len = nb; /* save a copy of the length for byte reversal */
-#endif
+	int err = 0;
+	int c;
 
-	/* unaligned, do this in pieces */
-	x = 0;
 	for (; nb > 0; nb -= c) {
-#ifdef __LITTLE_ENDIAN__
-		c = 1;
-#endif
-#ifdef __BIG_ENDIAN__
 		c = max_align(ea);
-#endif
 		if (c > nb)
 			c = max_align(nb);
-		err = read_mem_aligned(&b, ea, c);
+		switch (c) {
+		case 1:
+			err = __get_user(*dest, (unsigned char __user *) ea);
+			break;
+		case 2:
+			err = __get_user(*(u16 *)dest,
+					 (unsigned short __user *) ea);
+			break;
+		case 4:
+			err = __get_user(*(u32 *)dest,
+					 (unsigned int __user *) ea);
+			break;
+#ifdef __powerpc64__
+		case 8:
+			err = __get_user(*(unsigned long *)dest,
+					 (unsigned long __user *) ea);
+			break;
+#endif
+		}
 		if (err)
 			return err;
-		x = (x << (8 * c)) + b;
+		dest += c;
 		ea += c;
 	}
-#ifdef __LITTLE_ENDIAN__
-	switch (len) {
-	case 2:
-		*dest = byterev_2(x);
-		break;
-	case 4:
-		*dest = byterev_4(x);
-		break;
-#ifdef __powerpc64__
-	case 8:
-		*dest = byterev_8(x);
-		break;
-#endif
-	}
-#endif
-#ifdef __BIG_ENDIAN__
-	*dest = x;
-#endif
 	return 0;
 }
 
+static nokprobe_inline int read_mem_unaligned(unsigned long *dest,
+					      unsigned long ea, int nb,
+					      struct pt_regs *regs)
+{
+	union {
+		unsigned long ul;
+		u8 b[sizeof(unsigned long)];
+	} u;
+	int i;
+	int err;
+
+	u.ul = 0;
+	i = IS_BE ? sizeof(unsigned long) - nb : 0;
+	err = copy_mem_in(&u.b[i], ea, nb);
+	if (!err)
+		*dest = u.ul;
+	return err;
+}
+
 /*
  * Read memory at address ea for nb bytes, return 0 for success
- * or -EFAULT if an error occurred.
+ * or -EFAULT if an error occurred.  N.B. nb must be 1, 2, 4 or 8.
+ * If nb < sizeof(long), the result is right-justified on BE systems.
  */
 static int read_mem(unsigned long *dest, unsigned long ea, int nb,
 			      struct pt_regs *regs)
@@ -325,48 +337,64 @@ static nokprobe_inline int write_mem_aligned(unsigned long val,
 	return err;
 }
 
-static nokprobe_inline int write_mem_unaligned(unsigned long val,
-				unsigned long ea, int nb, struct pt_regs *regs)
+/*
+ * Copy from a buffer to userspace, using the largest possible
+ * aligned accesses, up to sizeof(long).
+ */
+static int nokprobe_inline copy_mem_out(u8 *dest, unsigned long ea, int nb)
 {
-	int err;
-	unsigned long c;
+	int err = 0;
+	int c;
 
-#ifdef __LITTLE_ENDIAN__
-	switch (nb) {
-	case 2:
-		val = byterev_2(val);
-		break;
-	case 4:
-		val = byterev_4(val);
-		break;
-#ifdef __powerpc64__
-	case 8:
-		val = byterev_8(val);
-		break;
-#endif
-	}
-#endif
-	/* unaligned or little-endian, do this in pieces */
 	for (; nb > 0; nb -= c) {
-#ifdef __LITTLE_ENDIAN__
-		c = 1;
-#endif
-#ifdef __BIG_ENDIAN__
 		c = max_align(ea);
-#endif
 		if (c > nb)
 			c = max_align(nb);
-		err = write_mem_aligned(val >> (nb - c) * 8, ea, c);
+		switch (c) {
+		case 1:
+			err = __put_user(*dest, (unsigned char __user *) ea);
+			break;
+		case 2:
+			err = __put_user(*(u16 *)dest,
+					 (unsigned short __user *) ea);
+			break;
+		case 4:
+			err = __put_user(*(u32 *)dest,
+					 (unsigned int __user *) ea);
+			break;
+#ifdef __powerpc64__
+		case 8:
+			err = __put_user(*(unsigned long *)dest,
+					 (unsigned long __user *) ea);
+			break;
+#endif
+		}
 		if (err)
 			return err;
+		dest += c;
 		ea += c;
 	}
 	return 0;
 }
 
+static nokprobe_inline int write_mem_unaligned(unsigned long val,
+					       unsigned long ea, int nb,
+					       struct pt_regs *regs)
+{
+	union {
+		unsigned long ul;
+		u8 b[sizeof(unsigned long)];
+	} u;
+	int i;
+
+	u.ul = val;
+	i = IS_BE ? sizeof(unsigned long) - nb : 0;
+	return copy_mem_out(&u.b[i], ea, nb);
+}
+
 /*
  * Write memory at address ea for nb bytes, return 0 for success
- * or -EFAULT if an error occurred.
+ * or -EFAULT if an error occurred.  N.B. nb must be 1, 2, 4 or 8.
  */
 static int write_mem(unsigned long val, unsigned long ea, int nb,
 			       struct pt_regs *regs)
@@ -389,40 +417,17 @@ static int do_fp_load(int rn, int (*func)(int, unsigned long),
 				struct pt_regs *regs)
 {
 	int err;
-	union {
-		double dbl;
-		unsigned long ul[2];
-		struct {
-#ifdef __BIG_ENDIAN__
-			unsigned _pad_;
-			unsigned word;
-#endif
-#ifdef __LITTLE_ENDIAN__
-			unsigned word;
-			unsigned _pad_;
-#endif
-		} single;
-	} data;
-	unsigned long ptr;
+	u8 buf[sizeof(double)] __attribute__((aligned(sizeof(double))));
 
 	if (!address_ok(regs, ea, nb))
 		return -EFAULT;
-	if ((ea & 3) == 0)
-		return (*func)(rn, ea);
-	ptr = (unsigned long) &data.ul;
-	if (sizeof(unsigned long) == 8 || nb == 4) {
-		err = read_mem_unaligned(&data.ul[0], ea, nb, regs);
-		if (nb == 4)
-			ptr = (unsigned long)&(data.single.word);
-	} else {
-		/* reading a double on 32-bit */
-		err = read_mem_unaligned(&data.ul[0], ea, 4, regs);
-		if (!err)
-			err = read_mem_unaligned(&data.ul[1], ea + 4, 4, regs);
+	if (ea & 3) {
+		err = copy_mem_in(buf, ea, nb);
+		if (err)
+			return err;
+		ea = (unsigned long) buf;
 	}
-	if (err)
-		return err;
-	return (*func)(rn, ptr);
+	return (*func)(rn, ea);
 }
 NOKPROBE_SYMBOL(do_fp_load);
 
@@ -431,43 +436,15 @@ static int do_fp_store(int rn, int (*func)(int, unsigned long),
 				 struct pt_regs *regs)
 {
 	int err;
-	union {
-		double dbl;
-		unsigned long ul[2];
-		struct {
-#ifdef __BIG_ENDIAN__
-			unsigned _pad_;
-			unsigned word;
-#endif
-#ifdef __LITTLE_ENDIAN__
-			unsigned word;
-			unsigned _pad_;
-#endif
-		} single;
-	} data;
-	unsigned long ptr;
+	u8 buf[sizeof(double)] __attribute__((aligned(sizeof(double))));
 
 	if (!address_ok(regs, ea, nb))
 		return -EFAULT;
 	if ((ea & 3) == 0)
 		return (*func)(rn, ea);
-	ptr = (unsigned long) &data.ul[0];
-	if (sizeof(unsigned long) == 8 || nb == 4) {
-		if (nb == 4)
-			ptr = (unsigned long)&(data.single.word);
-		err = (*func)(rn, ptr);
-		if (err)
-			return err;
-		err = write_mem_unaligned(data.ul[0], ea, nb, regs);
-	} else {
-		/* writing a double on 32-bit */
-		err = (*func)(rn, ptr);
-		if (err)
-			return err;
-		err = write_mem_unaligned(data.ul[0], ea, 4, regs);
-		if (!err)
-			err = write_mem_unaligned(data.ul[1], ea + 4, 4, regs);
-	}
+	err = (*func)(rn, (unsigned long) buf);
+	if (!err)
+		err = copy_mem_out(buf, ea, nb);
 	return err;
 }
 NOKPROBE_SYMBOL(do_fp_store);
@@ -2564,7 +2541,7 @@ int emulate_step(struct pt_regs *regs, unsigned int instr)
 #endif
 #ifdef CONFIG_VSX
 	case LOAD_VSX: {
-		char mem[16];
+		u8 mem[16];
 		union vsx_reg buf;
 		unsigned long msrbit = MSR_VSX;
 
@@ -2577,7 +2554,7 @@ int emulate_step(struct pt_regs *regs, unsigned int instr)
 		if (!(regs->msr & msrbit))
 			return 0;
 		if (!address_ok(regs, ea, size) ||
-		    __copy_from_user(mem, (void __user *)ea, size))
+		    copy_mem_in(mem, ea, size))
 			return 0;
 
 		emulate_vsx_load(&op, &buf, mem);
@@ -2639,7 +2616,7 @@ int emulate_step(struct pt_regs *regs, unsigned int instr)
 #endif
 #ifdef CONFIG_VSX
 	case STORE_VSX: {
-		char mem[16];
+		u8 mem[16];
 		union vsx_reg buf;
 		unsigned long msrbit = MSR_VSX;
 
@@ -2656,7 +2633,7 @@ int emulate_step(struct pt_regs *regs, unsigned int instr)
 
 		store_vsrn(op.reg, &buf);
 		emulate_vsx_store(&op, &buf, mem);
-		if (__copy_to_user((void __user *)ea, mem, size))
+		if (copy_mem_out(mem, ea, size))
 			return 0;
 		goto ldst_done;
 	}