riscv: make unsafe user copy routines use existing assembly routines

The current implementation is underperforming and in addition, it
triggers misaligned access traps on platforms which do not handle
misaligned accesses in hardware.

Use the existing assembly routines to solve both problems at once.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250602193918.868962-2-cleger@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>

Author: Alexandre Ghiti

arch/riscv/include/asm/asm-prototypes.h

@@ -12,7 +12,7 @@ long long __ashlti3(long long a, int b);
 #ifdef CONFIG_RISCV_ISA_V
 
 #ifdef CONFIG_MMU
-asmlinkage int enter_vector_usercopy(void *dst, void *src, size_t n);
+asmlinkage int enter_vector_usercopy(void *dst, void *src, size_t n, bool enable_sum);
 #endif /* CONFIG_MMU  */
 
 void xor_regs_2_(unsigned long bytes, unsigned long *__restrict p1,

arch/riscv/include/asm/uaccess.h

@@ -450,35 +450,18 @@ static inline void user_access_restore(unsigned long enabled) { }
 	(x) = (__force __typeof__(*(ptr)))__gu_val;			\
 } while (0)
 
-#define unsafe_copy_loop(dst, src, len, type, op, label)		\
-	while (len >= sizeof(type)) {					\
-		op(*(type *)(src), (type __user *)(dst), label);	\
-		dst += sizeof(type);					\
-		src += sizeof(type);					\
-		len -= sizeof(type);					\
-	}
+unsigned long __must_check __asm_copy_to_user_sum_enabled(void __user *to,
+	const void *from, unsigned long n);
+unsigned long __must_check __asm_copy_from_user_sum_enabled(void *to,
+	const void __user *from, unsigned long n);
 
 #define unsafe_copy_to_user(_dst, _src, _len, label)			\
-do {									\
-	char __user *__ucu_dst = (_dst);				\
-	const char *__ucu_src = (_src);					\
-	size_t __ucu_len = (_len);					\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u64, unsafe_put_user, label);	\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u32, unsafe_put_user, label);	\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u16, unsafe_put_user, label);	\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u8, unsafe_put_user, label);	\
-} while (0)
+	if (__asm_copy_to_user_sum_enabled(_dst, _src, _len))		\
+		goto label;
 
 #define unsafe_copy_from_user(_dst, _src, _len, label)			\
-do {									\
-	char *__ucu_dst = (_dst);					\
-	const char __user *__ucu_src = (_src);				\
-	size_t __ucu_len = (_len);					\
-	unsafe_copy_loop(__ucu_src, __ucu_dst, __ucu_len, u64, unsafe_get_user, label);	\
-	unsafe_copy_loop(__ucu_src, __ucu_dst, __ucu_len, u32, unsafe_get_user, label);	\
-	unsafe_copy_loop(__ucu_src, __ucu_dst, __ucu_len, u16, unsafe_get_user, label);	\
-	unsafe_copy_loop(__ucu_src, __ucu_dst, __ucu_len, u8, unsafe_get_user, label);	\
-} while (0)
+	if (__asm_copy_from_user_sum_enabled(_dst, _src, _len))		\
+		goto label;
 
 #else /* CONFIG_MMU */
 #include <asm-generic/uaccess.h>

arch/riscv/lib/riscv_v_helpers.c

@@ -16,8 +16,11 @@
 #ifdef CONFIG_MMU
 size_t riscv_v_usercopy_threshold = CONFIG_RISCV_ISA_V_UCOPY_THRESHOLD;
 int __asm_vector_usercopy(void *dst, void *src, size_t n);
+int __asm_vector_usercopy_sum_enabled(void *dst, void *src, size_t n);
 int fallback_scalar_usercopy(void *dst, void *src, size_t n);
-asmlinkage int enter_vector_usercopy(void *dst, void *src, size_t n)
+int fallback_scalar_usercopy_sum_enabled(void *dst, void *src, size_t n);
+asmlinkage int enter_vector_usercopy(void *dst, void *src, size_t n,
+				     bool enable_sum)
 {
 	size_t remain, copied;
 
@@ -26,7 +29,8 @@ asmlinkage int enter_vector_usercopy(void *dst, void *src, size_t n)
 		goto fallback;
 
 	kernel_vector_begin();
-	remain = __asm_vector_usercopy(dst, src, n);
+	remain = enable_sum ? __asm_vector_usercopy(dst, src, n) :
+			      __asm_vector_usercopy_sum_enabled(dst, src, n);
 	kernel_vector_end();
 
 	if (remain) {
@@ -40,6 +44,7 @@ asmlinkage int enter_vector_usercopy(void *dst, void *src, size_t n)
 	return remain;
 
 fallback:
-	return fallback_scalar_usercopy(dst, src, n);
+	return enable_sum ? fallback_scalar_usercopy(dst, src, n) :
+			    fallback_scalar_usercopy_sum_enabled(dst, src, n);
 }
 #endif

arch/riscv/lib/uaccess.S

@@ -17,14 +17,43 @@ SYM_FUNC_START(__asm_copy_to_user)
 	ALTERNATIVE("j fallback_scalar_usercopy", "nop", 0, RISCV_ISA_EXT_ZVE32X, CONFIG_RISCV_ISA_V)
 	REG_L	t0, riscv_v_usercopy_threshold
 	bltu	a2, t0, fallback_scalar_usercopy
-	tail enter_vector_usercopy
+	li	a3, 1
+	tail 	enter_vector_usercopy
 #endif
-SYM_FUNC_START(fallback_scalar_usercopy)
+SYM_FUNC_END(__asm_copy_to_user)
+EXPORT_SYMBOL(__asm_copy_to_user)
+SYM_FUNC_ALIAS(__asm_copy_from_user, __asm_copy_to_user)
+EXPORT_SYMBOL(__asm_copy_from_user)
 
+SYM_FUNC_START(fallback_scalar_usercopy)
 	/* Enable access to user memory */
-	li t6, SR_SUM
-	csrs CSR_STATUS, t6
+	li	t6, SR_SUM
+	csrs 	CSR_STATUS, t6
+	mv 	t6, ra
 
+	call 	fallback_scalar_usercopy_sum_enabled
+
+	/* Disable access to user memory */
+	mv 	ra, t6
+	li 	t6, SR_SUM
+	csrc 	CSR_STATUS, t6
+	ret
+SYM_FUNC_END(fallback_scalar_usercopy)
+
+SYM_FUNC_START(__asm_copy_to_user_sum_enabled)
+#ifdef CONFIG_RISCV_ISA_V
+	ALTERNATIVE("j fallback_scalar_usercopy_sum_enabled", "nop", 0, RISCV_ISA_EXT_ZVE32X, CONFIG_RISCV_ISA_V)
+	REG_L	t0, riscv_v_usercopy_threshold
+	bltu	a2, t0, fallback_scalar_usercopy_sum_enabled
+	li	a3, 0
+	tail 	enter_vector_usercopy
+#endif
+SYM_FUNC_END(__asm_copy_to_user_sum_enabled)
+SYM_FUNC_ALIAS(__asm_copy_from_user_sum_enabled, __asm_copy_to_user_sum_enabled)
+EXPORT_SYMBOL(__asm_copy_from_user_sum_enabled)
+EXPORT_SYMBOL(__asm_copy_to_user_sum_enabled)
+
+SYM_FUNC_START(fallback_scalar_usercopy_sum_enabled)
 	/*
 	 * Save the terminal address which will be used to compute the number
 	 * of bytes copied in case of a fixup exception.
@@ -178,23 +207,12 @@ SYM_FUNC_START(fallback_scalar_usercopy)
 	bltu	a0, t0, 4b	/* t0 - end of dst */
 
 .Lout_copy_user:
-	/* Disable access to user memory */
-	csrc CSR_STATUS, t6
 	li	a0, 0
 	ret
-
-	/* Exception fixup code */
 10:
-	/* Disable access to user memory */
-	csrc CSR_STATUS, t6
 	sub a0, t5, a0
 	ret
-SYM_FUNC_END(__asm_copy_to_user)
-SYM_FUNC_END(fallback_scalar_usercopy)
-EXPORT_SYMBOL(__asm_copy_to_user)
-SYM_FUNC_ALIAS(__asm_copy_from_user, __asm_copy_to_user)
-EXPORT_SYMBOL(__asm_copy_from_user)
-
+SYM_FUNC_END(fallback_scalar_usercopy_sum_enabled)
 
 SYM_FUNC_START(__clear_user)
 

arch/riscv/lib/uaccess_vector.S

@@ -24,7 +24,18 @@ SYM_FUNC_START(__asm_vector_usercopy)
 	/* Enable access to user memory */
 	li	t6, SR_SUM
 	csrs	CSR_STATUS, t6
+	mv	t6, ra
 
+	call 	__asm_vector_usercopy_sum_enabled
+
+	/* Disable access to user memory */
+	mv 	ra, t6
+	li 	t6, SR_SUM
+	csrc	CSR_STATUS, t6
+	ret
+SYM_FUNC_END(__asm_vector_usercopy)
+
+SYM_FUNC_START(__asm_vector_usercopy_sum_enabled)
 loop:
 	vsetvli iVL, iNum, e8, ELEM_LMUL_SETTING, ta, ma
 	fixup vle8.v vData, (pSrc), 10f
@@ -36,8 +47,6 @@ loop:
 
 	/* Exception fixup for vector load is shared with normal exit */
 10:
-	/* Disable access to user memory */
-	csrc	CSR_STATUS, t6
 	mv	a0, iNum
 	ret
 
@@ -49,4 +58,4 @@ loop:
 	csrr	t2, CSR_VSTART
 	sub	iNum, iNum, t2
 	j	10b
-SYM_FUNC_END(__asm_vector_usercopy)
+SYM_FUNC_END(__asm_vector_usercopy_sum_enabled)