[PATCH v4 2/2] powerpc/uaccess: Implement unsafe_copy_to_user() as a simple loop

Christophe Leroy
2020-04-17T17:08:59Z

At the time being, unsafe_copy_to_user() is based on
raw_copy_to_user() which calls __copy_tofrom_user().

__copy_tofrom_user() is a big optimised function to copy big amount
of data. It aligns destinations to cache line in order to use
dcbz instruction.

Today unsafe_copy_to_user() is called only from filldir().
It is used to mainly copy small amount of data like filenames,
so __copy_tofrom_user() is not fit.

Also, unsafe_copy_to_user() is used within user_access_begin/end
sections. In those section, it is preferable to not call functions.

Rewrite unsafe_copy_to_user() as a macro that uses __put_user_goto().
We first perform a loop of long, then we finish with necessary
complements.

unsafe_copy_to_user() might be used in the near future to copy
fixed-size data, like pt_regs structs during signal processing.
Having it as a macro allows GCC to optimise it for instead when
it knows the size in advance, it can unloop loops, drop complements
when the size is a multiple of longs, etc ...

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
v4: new
---
arch/powerpc/include/asm/uaccess.h | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 9365b59495a2..b24fbe75f9ce 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -514,7 +514,26 @@ static __must_check inline bool user_access_begin(const void __user *ptr, size_t
#define unsafe_op_wrap(op, err) do { if (unlikely(op)) goto err; } while (0)
#define unsafe_get_user(x, p, e) unsafe_op_wrap(__get_user_allowed(x, p), e)
#define unsafe_put_user(x, p, e) __put_user_goto(x, p, e)
+
#define unsafe_copy_to_user(d, s, l, e) \
- unsafe_op_wrap(raw_copy_to_user_allowed(d, s, l), e)
+do { \
+ u8 __user *_dst = (u8 __user *)(d); \
+ const u8 *_src = (const u8 *)(s); \
+ size_t _len = (l); \
+ int _i; \
+ \
+ for (_i = 0; _i < (_len & ~(sizeof(long) - 1)); _i += sizeof(long)) \
+ __put_user_goto(*(long*)(_src + _i), (long __user *)(_dst + _i), e);\
+ if (IS_ENABLED(CONFIG_PPC64) && (_len & 4)) { \
+ __put_user_goto(*(u32*)(_src + _i), (u32 __user *)(_dst + _i), e); \
+ _i += 4; \
+ } \
+ if (_len & 2) { \
+ __put_user_goto(*(u16*)(_src + _i), (u16 __user *)(_dst + _i), e); \
+ _i += 2; \
+ } \
+ if (_len & 1) \
+ __put_user_goto(*(u8*)(_src + _i), (u8 __user *)(_dst + _i), e);\
+} while (0)

#endif /* _ARCH_POWERPC_UACCESS_H */
--
2.25.0