s390/uaccess: Shorten raw_copy_from_user() / raw_copy_to_user() inline assemblies

Add specific exception handler for copy_to_user() / copy_from_user()
mvcos fault handling, which allows to shorten the inline assemblies to
three instructions.

On fault the exception handler adjusts the length used by the mvcos
instruction in a way that the instruction completes with condition code
zero, indicating the number of bytes copied with the input/output operand
'size'. This allows to calculate and return the number of bytes not copied,
if any, like required.

Loop and return value handling is changed to C so that the compiler may
optimize the code.

Signed-off-by: Heiko Carstens <[e-mail]>
Signed-off-by: Vasily Gorbik <[e-mail]>

arch/s390/include/asm/asm-extable.h

···
 #define EX_TYPE_UA_LOAD_REGPAIR	6
 #define EX_TYPE_ZEROPAD		7
 #define EX_TYPE_FPC		8
+#define EX_TYPE_UA_MVCOS_TO	9
+#define EX_TYPE_UA_MVCOS_FROM	10
 
 #define EX_DATA_REG_ERR_SHIFT	0
 #define EX_DATA_REG_ERR		GENMASK(3, 0)
···
 
 #define EX_TABLE_FPC(_fault, _target)					\
 	__EX_TABLE(__ex_table, _fault, _target, EX_TYPE_FPC, __stringify(%%r0), __stringify(%%r0), 0)
+
+#define EX_TABLE_UA_MVCOS_TO(_fault, _target)				\
+	__EX_TABLE(__ex_table, _fault, _target, EX_TYPE_UA_MVCOS_TO, __stringify(%%r0), __stringify(%%r0), 0)
+
+#define EX_TABLE_UA_MVCOS_FROM(_fault, _target)				\
+	__EX_TABLE(__ex_table, _fault, _target, EX_TYPE_UA_MVCOS_FROM, __stringify(%%r0), __stringify(%%r0), 0)
 
 #endif /* __ASM_EXTABLE_H */

arch/s390/include/asm/uaccess.h

···
 	};
 };
 
-static __always_inline __must_check unsigned long
+#ifdef CONFIG_KMSAN
+#define uaccess_kmsan_or_inline noinline __maybe_unused __no_sanitize_memory
+#else
+#define uaccess_kmsan_or_inline __always_inline
+#endif
+
+static uaccess_kmsan_or_inline __must_check unsigned long
 raw_copy_from_user_key(void *to, const void __user *from, unsigned long size, unsigned long key)
 {
-	unsigned long rem;
+	unsigned long osize;
 	union oac spec = {
 		.oac2.key = key,
 		.oac2.as = PSW_BITS_AS_SECONDARY,
 		.oac2.k = 1,
 		.oac2.a = 1,
 	};
+	int cc;
 
-	asm_inline volatile(
-		"	lr	%%r0,%[spec]\n"
-		"0:	mvcos	0(%[to]),0(%[from]),%[size]\n"
-		"1:	jz	5f\n"
-		"	algr	%[size],%[val]\n"
-		"	slgr	%[from],%[val]\n"
-		"	slgr	%[to],%[val]\n"
-		"	j	0b\n"
-		"2:	la	%[rem],4095(%[from])\n" /* rem = from + 4095 */
-		"	nr	%[rem],%[val]\n"	/* rem = (from + 4095) & -4096 */
-		"	slgr	%[rem],%[from]\n"
-		"	clgr	%[size],%[rem]\n"	/* copy crosses next page boundary? */
-		"	jnh	6f\n"
-		"3:	mvcos	0(%[to]),0(%[from]),%[rem]\n"
-		"4:	slgr	%[size],%[rem]\n"
-		"	j	6f\n"
-		"5:	lghi	%[size],0\n"
-		"6:\n"
-		EX_TABLE(0b, 2b)
-		EX_TABLE(1b, 2b)
-		EX_TABLE(3b, 6b)
-		EX_TABLE(4b, 6b)
-		: [size] "+&a" (size), [from] "+&a" (from), [to] "+&a" (to), [rem] "=&a" (rem)
-		: [val] "a" (-4096UL), [spec] "d" (spec.val)
-		: "cc", "memory", "0");
-	return size;
+	while (1) {
+		osize = size;
+		asm_inline volatile(
+			"	lr	%%r0,%[spec]\n"
+			"0:	mvcos	%[to],%[from],%[size]\n"
+			"1:	nopr	%%r7\n"
+			CC_IPM(cc)
+			EX_TABLE_UA_MVCOS_FROM(0b, 0b)
+			EX_TABLE_UA_MVCOS_FROM(1b, 0b)
+			: CC_OUT(cc, cc), [size] "+d" (size), [to] "=Q" (*(char *)to)
+			: [spec] "d" (spec.val), [from] "Q" (*(const char __user *)from)
+			: CC_CLOBBER_LIST("memory", "0"));
+		if (likely(CC_TRANSFORM(cc) == 0))
+			return osize - size;
+		size -= 4096;
+		to += 4096;
+		from += 4096;
+	}
 }
 
 static __always_inline __must_check unsigned long
···
 	return raw_copy_from_user_key(to, from, n, 0);
 }
 
-static __always_inline __must_check unsigned long
+static uaccess_kmsan_or_inline __must_check unsigned long
 raw_copy_to_user_key(void __user *to, const void *from, unsigned long size, unsigned long key)
 {
-	unsigned long rem;
+	unsigned long osize;
 	union oac spec = {
 		.oac1.key = key,
 		.oac1.as = PSW_BITS_AS_SECONDARY,
 		.oac1.k = 1,
 		.oac1.a = 1,
 	};
+	int cc;
 
-	asm_inline volatile(
-		"	lr	%%r0,%[spec]\n"
-		"0:	mvcos	0(%[to]),0(%[from]),%[size]\n"
-		"1:	jz	5f\n"
-		"	algr	%[size],%[val]\n"
-		"	slgr	%[to],%[val]\n"
-		"	slgr	%[from],%[val]\n"
-		"	j	0b\n"
-		"2:	la	%[rem],4095(%[to])\n"	/* rem = to + 4095 */
-		"	nr	%[rem],%[val]\n"	/* rem = (to + 4095) & -4096 */
-		"	slgr	%[rem],%[to]\n"
-		"	clgr	%[size],%[rem]\n"	/* copy crosses next page boundary? */
-		"	jnh	6f\n"
-		"3:	mvcos	0(%[to]),0(%[from]),%[rem]\n"
-		"4:	slgr	%[size],%[rem]\n"
-		"	j	6f\n"
-		"5:	lghi	%[size],0\n"
-		"6:\n"
-		EX_TABLE(0b, 2b)
-		EX_TABLE(1b, 2b)
-		EX_TABLE(3b, 6b)
-		EX_TABLE(4b, 6b)
-		: [size] "+&a" (size), [to] "+&a" (to), [from] "+&a" (from), [rem] "=&a" (rem)
-		: [val] "a" (-4096UL), [spec] "d" (spec.val)
-		: "cc", "memory", "0");
-	return size;
+	while (1) {
+		osize = size;
+		asm_inline volatile(
+			"	lr	%%r0,%[spec]\n"
+			"0:	mvcos	%[to],%[from],%[size]\n"
+			"1:	nopr	%%r7\n"
+			CC_IPM(cc)
+			EX_TABLE_UA_MVCOS_TO(0b, 0b)
+			EX_TABLE_UA_MVCOS_TO(1b, 0b)
+			: CC_OUT(cc, cc), [size] "+d" (size), [to] "=Q" (*(char __user *)to)
+			: [spec] "d" (spec.val), [from] "Q" (*(const char *)from)
+			: CC_CLOBBER_LIST("memory", "0"));
+		if (likely(CC_TRANSFORM(cc) == 0))
+			return osize - size;
+		size -= 4096;
+		to += 4096;
+		from += 4096;
+	}
 }
 
 static __always_inline __must_check unsigned long
···
 }
 
 int __noreturn __put_user_bad(void);
-
-#ifdef CONFIG_KMSAN
-#define uaccess_kmsan_or_inline noinline __maybe_unused __no_sanitize_memory
-#else
-#define uaccess_kmsan_or_inline __always_inline
-#endif
 
 #ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
 

arch/s390/mm/extable.c

···
 	return true;
 }
 
+struct insn_ssf {
+	u64	opc1 : 8;
+	u64	r3   : 4;
+	u64	opc2 : 4;
+	u64	b1   : 4;
+	u64	d1   : 12;
+	u64	b2   : 4;
+	u64	d2   : 12;
+} __packed;
+
+static bool ex_handler_ua_mvcos(const struct exception_table_entry *ex,
+				bool from, struct pt_regs *regs)
+{
+	unsigned long uaddr, remainder;
+	struct insn_ssf *insn;
+
+	/*
+	 * If the faulting user space access crossed a page boundary retry by
+	 * limiting the access to the first page (adjust length accordingly).
+	 * Then the mvcos instruction will either complete with condition code
+	 * zero, or generate another fault where the user space access did not
+	 * cross a page boundary.
+	 * If the faulting user space access did not cross a page boundary set
+	 * length to zero and retry. In this case no user space access will
+	 * happen, and the mvcos instruction will complete with condition code
+	 * zero.
+	 * In both cases the instruction will complete with condition code
+	 * zero (copying finished), and the register which contains the
+	 * length, indicates the number of bytes copied.
+	 */
+	regs->psw.addr = extable_fixup(ex);
+	insn = (struct insn_ssf *)regs->psw.addr;
+	if (from)
+		uaddr = regs->gprs[insn->b2] + insn->d2;
+	else
+		uaddr = regs->gprs[insn->b1] + insn->d1;
+	remainder = PAGE_SIZE - (uaddr & (PAGE_SIZE - 1));
+	if (regs->gprs[insn->r3] <= remainder)
+		remainder = 0;
+	regs->gprs[insn->r3] = remainder;
+	return true;
+}
+
 bool fixup_exception(struct pt_regs *regs)
 {
 	const struct exception_table_entry *ex;
···
 		return ex_handler_zeropad(ex, regs);
 	case EX_TYPE_FPC:
 		return ex_handler_fpc(ex, regs);
+	case EX_TYPE_UA_MVCOS_TO:
+		return ex_handler_ua_mvcos(ex, false, regs);
+	case EX_TYPE_UA_MVCOS_FROM:
+		return ex_handler_ua_mvcos(ex, true, regs);
 	}
 	panic("invalid exception table entry");
 }