Re: [PATCH 2/8] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 15/10/2020 à 17:01, Christopher M. Riedl a écrit :
> Reuse the "safe" implementation from signal.c except for calling
> unsafe_copy_from_user() to copy into a local buffer. Unlike the
> unsafe_copy_{vsx,fpr}_to_user() functions the "copy from" functions
> cannot use unsafe_get_user() directly to bypass the local buffer since
> doing so significantly reduces signal handling performance.

Why can't the functions use unsafe_get_user(), why does it significantly reduces signal handling 
performance ? How much significant ? I would expect that not going through an intermediate memory 
area would be more efficient

Christophe


> 
> Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
> ---
>   arch/powerpc/kernel/signal.h | 33 +++++++++++++++++++++++++++++++++
>   1 file changed, 33 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
> index 2559a681536e..e9aaeac0da37 100644
> --- a/arch/powerpc/kernel/signal.h
> +++ b/arch/powerpc/kernel/signal.h
> @@ -53,6 +53,33 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
>   				&buf[i], label);\
>   } while (0)
>   
> +#define unsafe_copy_fpr_from_user(task, from, label)	do {		\
> +	struct task_struct *__t = task;					\
> +	u64 __user *__f = (u64 __user *)from;				\
> +	u64 buf[ELF_NFPREG];						\
> +	int i;								\
> +									\
> +	unsafe_copy_from_user(buf, __f, ELF_NFPREG * sizeof(double),	\
> +				label);					\
> +	for (i = 0; i < ELF_NFPREG - 1; i++)				\
> +		__t->thread.TS_FPR(i) = buf[i];				\
> +	__t->thread.fp_state.fpscr = buf[i];				\
> +} while (0)
> +
> +#define unsafe_copy_vsx_from_user(task, from, label)	do {		\
> +	struct task_struct *__t = task;					\
> +	u64 __user *__f = (u64 __user *)from;				\
> +	u64 buf[ELF_NVSRHALFREG];					\
> +	int i;								\
> +									\
> +	unsafe_copy_from_user(buf, __f,					\
> +				ELF_NVSRHALFREG * sizeof(double),	\
> +				label);					\
> +	for (i = 0; i < ELF_NVSRHALFREG ; i++)				\
> +		__t->thread.fp_state.fpr[i][TS_VSRLOWOFFSET] = buf[i];	\
> +} while (0)
> +
> +
>   #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
>   #define unsafe_copy_ckfpr_to_user(to, task, label)	do {		\
>   	struct task_struct *__t = task;					\
> @@ -80,6 +107,10 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
>   	unsafe_copy_to_user(to, (task)->thread.fp_state.fpr,	\
>   			    ELF_NFPREG * sizeof(double), label)
>   
> +#define unsafe_copy_fpr_from_user(task, from, label)		\
> +	unsafe_copy_from_user((task)->thread.fp_state.fpr, from	\
> +			    ELF_NFPREG * sizeof(double), label)
> +
>   static inline unsigned long
>   copy_fpr_to_user(void __user *to, struct task_struct *task)
>   {
> @@ -115,6 +146,8 @@ copy_ckfpr_from_user(struct task_struct *task, void __user *from)
>   #else
>   #define unsafe_copy_fpr_to_user(to, task, label) do { } while (0)
>   
> +#define unsafe_copy_fpr_from_user(task, from, label) do { } while (0)
> +
>   static inline unsigned long
>   copy_fpr_to_user(void __user *to, struct task_struct *task)
>   {
>