diff options
| author | Michael Ellerman <mpe@ellerman.id.au> | 2018-11-29 09:42:24 +0300 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2019-02-23 14:31:39 +0300 |
| commit | e7fda7e569e1776d4dccbcef52d34882b62b0654 (patch) | |
| tree | 06c73856748dd3aa8a2a82aca4df35c9c8c801f1 /arch/powerpc/kernel | |
| parent | fb0b0a73b223fc113e961b1d921322844e9c30d9 (diff) | |
| download | linux-e7fda7e569e1776d4dccbcef52d34882b62b0654.tar.xz | |
powerpc/64s: Remove MSR_RI optimisation in system_call_exit()
Currently in system_call_exit() we have an optimisation where we
disable MSR_RI (recoverable interrupt) and MSR_EE (external interrupt
enable) in a single mtmsrd instruction.
Unfortunately this will no longer work with THREAD_INFO_IN_TASK,
because then the load of TI_FLAGS might fault and faulting with MSR_RI
clear is treated as an unrecoverable exception which leads to a
panic().
So change the code to only clear MSR_EE prior to loading TI_FLAGS,
leaving the clear of MSR_RI until later. We have some latitude in
where do the clear of MSR_RI. A bit of experimentation has shown that
this location gives the least slow down.
This still causes a noticeable slow down in our null_syscall
performance. On a Power9 DD2.2:
Before After Delta Delta %
955 cycles 999 cycles -44 -4.6%
On the plus side this does simplify the code somewhat, because we
don't have to reenable MSR_RI on the restore_math() or
syscall_exit_work() paths which was necessitated previously by the
optimisation.
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/kernel')
| -rw-r--r-- | arch/powerpc/kernel/entry_64.S | 34 |
1 files changed, 14 insertions, 20 deletions
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index a2c168b395d2..c17c1bed6148 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -236,18 +236,14 @@ system_call_exit: /* * Disable interrupts so current_thread_info()->flags can't change, * and so that we don't get interrupted after loading SRR0/1. + * + * Leave MSR_RI enabled for now, because with THREAD_INFO_IN_TASK we + * could fault on the load of the TI_FLAGS below. */ #ifdef CONFIG_PPC_BOOK3E wrteei 0 #else - /* - * For performance reasons we clear RI the same time that we - * clear EE. We only need to clear RI just before we restore r13 - * below, but batching it with EE saves us one expensive mtmsrd call. - * We have to be careful to restore RI if we branch anywhere from - * here (eg syscall_exit_work). - */ - li r11,0 + li r11,MSR_RI mtmsrd r11,1 #endif /* CONFIG_PPC_BOOK3E */ @@ -263,15 +259,7 @@ system_call_exit: bne 3f #endif 2: addi r3,r1,STACK_FRAME_OVERHEAD -#ifdef CONFIG_PPC_BOOK3S - li r10,MSR_RI - mtmsrd r10,1 /* Restore RI */ -#endif bl restore_math -#ifdef CONFIG_PPC_BOOK3S - li r11,0 - mtmsrd r11,1 -#endif ld r8,_MSR(r1) ld r3,RESULT(r1) li r11,-MAX_ERRNO @@ -287,6 +275,16 @@ END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS) andi. r6,r8,MSR_PR ld r4,_LINK(r1) +#ifdef CONFIG_PPC_BOOK3S + /* + * Clear MSR_RI, MSR_EE is already and remains disabled. We could do + * this later, but testing shows that doing it here causes less slow + * down than doing it closer to the rfid. + */ + li r11,0 + mtmsrd r11,1 +#endif + beq- 1f ACCOUNT_CPU_USER_EXIT(r13, r11, r12) @@ -363,10 +361,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) b .Lsyscall_exit .Lsyscall_exit_work: -#ifdef CONFIG_PPC_BOOK3S - li r10,MSR_RI - mtmsrd r10,1 /* Restore RI */ -#endif /* If TIF_RESTOREALL is set, don't scribble on either r3 or ccr. If TIF_NOERROR is set, just save r3 as it is. */ |