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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>
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fb0b0a73b2
commit
e7fda7e569
1 changed files with 14 additions and 20 deletions
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@ -236,18 +236,14 @@ system_call_exit:
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/*
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/*
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* Disable interrupts so current_thread_info()->flags can't change,
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* Disable interrupts so current_thread_info()->flags can't change,
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* and so that we don't get interrupted after loading SRR0/1.
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* and so that we don't get interrupted after loading SRR0/1.
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*
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* Leave MSR_RI enabled for now, because with THREAD_INFO_IN_TASK we
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* could fault on the load of the TI_FLAGS below.
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*/
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*/
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#ifdef CONFIG_PPC_BOOK3E
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#ifdef CONFIG_PPC_BOOK3E
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wrteei 0
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wrteei 0
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#else
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#else
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/*
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li r11,MSR_RI
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* For performance reasons we clear RI the same time that we
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* clear EE. We only need to clear RI just before we restore r13
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* below, but batching it with EE saves us one expensive mtmsrd call.
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* We have to be careful to restore RI if we branch anywhere from
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* here (eg syscall_exit_work).
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*/
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li r11,0
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mtmsrd r11,1
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mtmsrd r11,1
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#endif /* CONFIG_PPC_BOOK3E */
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#endif /* CONFIG_PPC_BOOK3E */
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@ -263,15 +259,7 @@ system_call_exit:
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bne 3f
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bne 3f
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#endif
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#endif
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2: addi r3,r1,STACK_FRAME_OVERHEAD
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2: addi r3,r1,STACK_FRAME_OVERHEAD
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#ifdef CONFIG_PPC_BOOK3S
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li r10,MSR_RI
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mtmsrd r10,1 /* Restore RI */
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#endif
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bl restore_math
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bl restore_math
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#ifdef CONFIG_PPC_BOOK3S
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li r11,0
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mtmsrd r11,1
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#endif
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ld r8,_MSR(r1)
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ld r8,_MSR(r1)
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ld r3,RESULT(r1)
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ld r3,RESULT(r1)
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li r11,-MAX_ERRNO
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li r11,-MAX_ERRNO
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@ -287,6 +275,16 @@ END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
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andi. r6,r8,MSR_PR
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andi. r6,r8,MSR_PR
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ld r4,_LINK(r1)
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ld r4,_LINK(r1)
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#ifdef CONFIG_PPC_BOOK3S
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/*
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* Clear MSR_RI, MSR_EE is already and remains disabled. We could do
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* this later, but testing shows that doing it here causes less slow
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* down than doing it closer to the rfid.
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*/
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li r11,0
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mtmsrd r11,1
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#endif
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beq- 1f
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beq- 1f
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ACCOUNT_CPU_USER_EXIT(r13, r11, r12)
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ACCOUNT_CPU_USER_EXIT(r13, r11, r12)
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@ -363,10 +361,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
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b .Lsyscall_exit
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b .Lsyscall_exit
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.Lsyscall_exit_work:
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.Lsyscall_exit_work:
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#ifdef CONFIG_PPC_BOOK3S
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li r10,MSR_RI
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mtmsrd r10,1 /* Restore RI */
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#endif
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/* If TIF_RESTOREALL is set, don't scribble on either r3 or ccr.
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/* If TIF_RESTOREALL is set, don't scribble on either r3 or ccr.
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If TIF_NOERROR is set, just save r3 as it is. */
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If TIF_NOERROR is set, just save r3 as it is. */
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