Re: [PATCH v5 17/22] powerpc/syscall: Do not check unsupported scv vector on PPC32

Nicholas Piggin
2021-02-09T02:01:39Z

Excerpts from Christophe Leroy's message of February 9, 2021 1:10 am:
> Only PPC64 has scv. No need to check the 0x7ff0 trap on PPC32.
> For that, add a helper trap_is_unsupported_scv() similar to
> trap_is_scv().
>
> And ignore the scv parameter in syscall_exit_prepare (Save 14 cycles
> 346 => 332 cycles)
>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
> v5: Added a helper trap_is_unsupported_scv()
> ---
> arch/powerpc/include/asm/ptrace.h | 5 +++++
> arch/powerpc/kernel/entry_32.S | 1 -
> arch/powerpc/kernel/interrupt.c | 7 +++++--
> 3 files changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
> index 58f9dc060a7b..2c842b11a924 100644
> --- a/arch/powerpc/include/asm/ptrace.h
> +++ b/arch/powerpc/include/asm/ptrace.h
> @@ -229,6 +229,11 @@ static inline bool trap_is_scv(struct pt_regs *regs)
> return (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && TRAP(regs) == 0x3000);
> }
>
> +static inline bool trap_is_unsupported_scv(struct pt_regs *regs)
> +{
> + return (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && TRAP(regs) == 0x7ff0);
> +}

This change is good.

> +
> static inline bool trap_is_syscall(struct pt_regs *regs)
> {
> return (trap_is_scv(regs) || TRAP(regs) == 0xc00);
> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
> index cffe58e63356..7c824e8928d0 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -344,7 +344,6 @@ transfer_to_syscall:
>
> ret_from_syscall:
> addi r4,r1,STACK_FRAME_OVERHEAD
> - li r5,0
> bl syscall_exit_prepare

For this one, I think it would be nice to do the "right" thing and make
the function prototypes different on !64S. They could then declare a
local const bool scv = 0.

We could have syscall_exit_prepare and syscall_exit_prepare_maybe_scv
or something like that, 64s can use the latter one and the former can be
a wrapper that passes constant 0 for scv. Then we don't have different
prototypes for the same function, but you just have to make the 32-bit
version static inline and the 64-bit version exported to asm.

Thanks,
Nick

> #if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
> /* If the process has its own DBCR0 value, load it up. The internal
> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
> index 205902052112..8fafca727b8b 100644
> --- a/arch/powerpc/kernel/interrupt.c
> +++ b/arch/powerpc/kernel/interrupt.c
> @@ -88,7 +88,7 @@ notrace long system_call_exception(long r3, long r4, long r5,
> local_irq_enable();
>
> if (unlikely(current_thread_info()->flags & _TIF_SYSCALL_DOTRACE)) {
> - if (unlikely(regs->trap == 0x7ff0)) {
> + if (unlikely(trap_is_unsupported_scv(regs))) {
> /* Unsupported scv vector */
> _exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
> return regs->gpr[3];
> @@ -111,7 +111,7 @@ notrace long system_call_exception(long r3, long r4, long r5,
> r8 = regs->gpr[8];
>
> } else if (unlikely(r0 >= NR_syscalls)) {
> - if (unlikely(regs->trap == 0x7ff0)) {
> + if (unlikely(trap_is_unsupported_scv(regs))) {
> /* Unsupported scv vector */
> _exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
> return regs->gpr[3];
> @@ -224,6 +224,9 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
> unsigned long ti_flags;
> unsigned long ret = 0;
>
> + if (IS_ENABLED(CONFIG_PPC32))
> + scv = 0;
> +
> CT_WARN_ON(ct_state() == CONTEXT_USER);
>
> #ifdef CONFIG_PPC64
> --
> 2.25.0
>
>