On Fri Oct 16, 2020 at 10:48 AM CDT, Christophe Leroy wrote:
>
>
> 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
>
Here is a comparison, 'unsafe-signal64-regs' avoids the intermediate buffer:
| | hash | radix |
| -------------------- | ------ | ------ |
| linuxppc/next | 289014 | 158408 |
| unsafe-signal64 | 298506 | 253053 |
| unsafe-signal64-regs | 254898 | 220831 |
I have not figured out the 'why' yet. As you mentioned in your series,
technically calling __copy_tofrom_user() is overkill for these
operations. The only obvious difference between unsafe_put_user() and
unsafe_get_user() is that we don't have asm-goto for the 'get' variant.
Instead we wrap with unsafe_op_wrap() which inserts a conditional and
then goto to the label.
Implemenations:
#define unsafe_copy_fpr_from_user(task, from, label) do { \
struct task_struct *__t = task; \
u64 __user *buf = (u64 __user *)from; \
int i; \
\
for (i = 0; i < ELF_NFPREG - 1; i++) \
unsafe_get_user(__t->thread.TS_FPR(i), &buf[i], label); \
unsafe_get_user(__t->thread.fp_state.fpscr, &buf[i], label); \
} while (0)
#define unsafe_copy_vsx_from_user(task, from, label) do { \
struct task_struct *__t = task; \
u64 __user *buf = (u64 __user *)from; \
int i; \
\
for (i = 0; i < ELF_NVSRHALFREG ; i++) \
unsafe_get_user(__t->thread.fp_state.fpr[i][TS_VSRLOWOFFSET], \
&buf[i], label); \
} while (0)
> Christophe
>
>
> >
> > Signed-off-by: Christopher M. Riedl <c...@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)
> > {
> >
