[PATCH v2 10/14] powerpc: Provide syscall wrapper

[Christophe Leroy]

Le 25/07/2022 à 08:30, Rohan McLure a écrit :
> Implement syscall wrapper as per s390, x86, arm64. When enabled
> cause handlers to accept parameters from a stack frame rather than
> from user scratch register state. This allows for user registers to be
> safely cleared in order to reduce caller influence on speculation
> within syscall routine. The wrapper is a macro that emits syscall
> handler symbols that call into the target handler, obtaining its
> parameters from a struct pt_regs on the stack.
> 
> As registers are already saved to the stack prior to calling
> system_call_exception, it appears that this function is executed more
> efficiently with the new stack-pointer convention than with parameters
> passed by registers, avoiding the allocation of a stack frame for this
> method. On a 32-bit system, we see >20% performance increases on the
> null_syscall microbenchmark, and on a Power 8 the performance gains
> amortise the cost of clearing and restoring registers which is
> implemented at the end of this series, seeing final result of ~5.6%
> performance improvement on null_syscall.
> 
> Syscalls are wrapped in this fashion on all platforms except for the
> Cell processor as this commit does not provide SPU support. This can be
> quickly fixed in a successive patch, but requires spu_sys_callback to
> allocate a pt_regs structure to satisfy the wrapped calling convention.
> 
> Co-developed-by: Andrew Donnellan <ajd at linux.ibm.com>
> Signed-off-by: Andrew Donnellan <ajd at linux.ibm.com>
> Signed-off-by: Rohan McLure <rmclure at linux.ibm.com>
> ---
> V1 -> V2: Generate prototypes for symbols produced by the wrapper.
> ---
>   arch/powerpc/Kconfig                       |  1 +
>   arch/powerpc/include/asm/interrupt.h       |  3 +-
>   arch/powerpc/include/asm/syscall.h         |  4 +
>   arch/powerpc/include/asm/syscall_wrapper.h | 94 ++++++++++++++++++++
>   arch/powerpc/include/asm/syscalls.h        | 25 +++++-
>   arch/powerpc/kernel/entry_32.S             |  6 +-
>   arch/powerpc/kernel/interrupt.c            | 31 +++----
>   arch/powerpc/kernel/interrupt_64.S         | 30 +++----
>   arch/powerpc/kernel/systbl.c               |  2 +
>   arch/powerpc/kernel/vdso.c                 |  2 +
>   10 files changed, 156 insertions(+), 42 deletions(-)
> 

This patch doesn't apply on powerpc tree, conflicts with 1547db7d1f44 
("powerpc: Move system_call_exception() to syscall.c")

Christophe