s390: add options to change branch prediction behaviour for the kernel
Add the PPA instruction to the system entry and exit path to switch the kernel to a different branch prediction behaviour. The instructions are added via CPU alternatives and can be disabled with the "nospec" or the "nobp=0" kernel parameter. If the default behaviour selected with CONFIG_KERNEL_NOBP is set to "n" then the "nobp=1" parameter can be used to enable the changed kernel branch prediction. Acked-by: Cornelia Huck <cohuck@redhat.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky
parent
cf14899846
commit
d768bd892f
@ -540,6 +540,23 @@ config ARCH_RANDOM
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If unsure, say Y.
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config KERNEL_NOBP
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def_bool n
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prompt "Enable modified branch prediction for the kernel by default"
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help
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If this option is selected the kernel will switch to a modified
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branch prediction mode if the firmware interface is available.
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The modified branch prediction mode improves the behaviour in
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regard to speculative execution.
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With the option enabled the kernel parameter "nobp=0" or "nospec"
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can be used to run the kernel in the normal branch prediction mode.
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With the option disabled the modified branch prediction mode is
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enabled with the "nobp=1" kernel parameter.
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If unsure, say N.
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endmenu
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menu "Memory setup"
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@ -91,6 +91,7 @@ void cpu_detect_mhz_feature(void);
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extern const struct seq_operations cpuinfo_op;
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extern int sysctl_ieee_emulation_warnings;
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extern void execve_tail(void);
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extern void __bpon(void);
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/*
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* User space process size: 2GB for 31 bit, 4TB or 8PT for 64 bit.
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@ -15,6 +15,29 @@ static int __init disable_alternative_instructions(char *str)
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early_param("noaltinstr", disable_alternative_instructions);
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static int __init nobp_setup_early(char *str)
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{
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bool enabled;
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int rc;
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rc = kstrtobool(str, &enabled);
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if (rc)
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return rc;
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if (enabled && test_facility(82))
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__set_facility(82, S390_lowcore.alt_stfle_fac_list);
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else
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__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
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return 0;
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}
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early_param("nobp", nobp_setup_early);
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static int __init nospec_setup_early(char *str)
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{
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__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
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return 0;
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}
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early_param("nospec", nospec_setup_early);
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struct brcl_insn {
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u16 opc;
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s32 disp;
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@ -196,6 +196,8 @@ static noinline __init void setup_facility_list(void)
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memcpy(S390_lowcore.alt_stfle_fac_list,
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S390_lowcore.stfle_fac_list,
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sizeof(S390_lowcore.alt_stfle_fac_list));
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if (!IS_ENABLED(CONFIG_KERNEL_NOBP))
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__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
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}
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static __init void detect_diag9c(void)
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@ -159,6 +159,34 @@ _PIF_WORK = (_PIF_PER_TRAP | _PIF_SYSCALL_RESTART)
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tm off+\addr, \mask
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.endm
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.macro BPOFF
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.pushsection .altinstr_replacement, "ax"
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660: .long 0xb2e8c000
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.popsection
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661: .long 0x47000000
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.pushsection .altinstructions, "a"
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.long 661b - .
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.long 660b - .
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.word 82
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.byte 4
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.byte 4
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.popsection
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.endm
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.macro BPON
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.pushsection .altinstr_replacement, "ax"
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662: .long 0xb2e8d000
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.popsection
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663: .long 0x47000000
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.pushsection .altinstructions, "a"
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.long 663b - .
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.long 662b - .
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.word 82
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.byte 4
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.byte 4
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.popsection
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.endm
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.section .kprobes.text, "ax"
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.Ldummy:
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/*
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@ -171,6 +199,11 @@ _PIF_WORK = (_PIF_PER_TRAP | _PIF_SYSCALL_RESTART)
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*/
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nop 0
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ENTRY(__bpon)
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.globl __bpon
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BPON
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br %r14
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/*
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* Scheduler resume function, called by switch_to
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* gpr2 = (task_struct *) prev
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@ -226,8 +259,11 @@ ENTRY(sie64a)
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jnz .Lsie_skip
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TSTMSK __LC_CPU_FLAGS,_CIF_FPU
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jo .Lsie_skip # exit if fp/vx regs changed
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BPON
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.Lsie_entry:
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sie 0(%r14)
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.Lsie_exit:
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BPOFF
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.Lsie_skip:
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ni __SIE_PROG0C+3(%r14),0xfe # no longer in SIE
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lctlg %c1,%c1,__LC_USER_ASCE # load primary asce
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@ -279,6 +315,7 @@ ENTRY(system_call)
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stpt __LC_SYNC_ENTER_TIMER
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.Lsysc_stmg:
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stmg %r8,%r15,__LC_SAVE_AREA_SYNC
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BPOFF
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lg %r12,__LC_CURRENT
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lghi %r13,__TASK_thread
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lghi %r14,_PIF_SYSCALL
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@ -325,6 +362,7 @@ ENTRY(system_call)
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jnz .Lsysc_work # check for work
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TSTMSK __LC_CPU_FLAGS,_CIF_WORK
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jnz .Lsysc_work
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BPON
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.Lsysc_restore:
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lg %r14,__LC_VDSO_PER_CPU
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lmg %r0,%r10,__PT_R0(%r11)
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@ -530,6 +568,7 @@ ENTRY(kernel_thread_starter)
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ENTRY(pgm_check_handler)
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stpt __LC_SYNC_ENTER_TIMER
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BPOFF
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stmg %r8,%r15,__LC_SAVE_AREA_SYNC
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lg %r10,__LC_LAST_BREAK
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lg %r12,__LC_CURRENT
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@ -637,6 +676,7 @@ ENTRY(pgm_check_handler)
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ENTRY(io_int_handler)
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STCK __LC_INT_CLOCK
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stpt __LC_ASYNC_ENTER_TIMER
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BPOFF
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stmg %r8,%r15,__LC_SAVE_AREA_ASYNC
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lg %r12,__LC_CURRENT
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larl %r13,cleanup_critical
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@ -687,9 +727,13 @@ ENTRY(io_int_handler)
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lg %r14,__LC_VDSO_PER_CPU
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lmg %r0,%r10,__PT_R0(%r11)
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mvc __LC_RETURN_PSW(16),__PT_PSW(%r11)
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tm __PT_PSW+1(%r11),0x01 # returning to user ?
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jno .Lio_exit_kernel
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BPON
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.Lio_exit_timer:
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stpt __LC_EXIT_TIMER
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mvc __VDSO_ECTG_BASE(16,%r14),__LC_EXIT_TIMER
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.Lio_exit_kernel:
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lmg %r11,%r15,__PT_R11(%r11)
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lpswe __LC_RETURN_PSW
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.Lio_done:
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@ -860,6 +904,7 @@ ENTRY(io_int_handler)
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ENTRY(ext_int_handler)
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STCK __LC_INT_CLOCK
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stpt __LC_ASYNC_ENTER_TIMER
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BPOFF
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stmg %r8,%r15,__LC_SAVE_AREA_ASYNC
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lg %r12,__LC_CURRENT
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larl %r13,cleanup_critical
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@ -908,6 +953,7 @@ ENTRY(psw_idle)
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.Lpsw_idle_stcctm:
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#endif
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oi __LC_CPU_FLAGS+7,_CIF_ENABLED_WAIT
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BPON
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STCK __CLOCK_IDLE_ENTER(%r2)
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stpt __TIMER_IDLE_ENTER(%r2)
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.Lpsw_idle_lpsw:
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@ -1008,6 +1054,7 @@ load_fpu_regs:
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*/
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ENTRY(mcck_int_handler)
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STCK __LC_MCCK_CLOCK
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BPOFF
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la %r1,4095 # validate r1
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spt __LC_CPU_TIMER_SAVE_AREA-4095(%r1) # validate cpu timer
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sckc __LC_CLOCK_COMPARATOR # validate comparator
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@ -1118,6 +1165,7 @@ ENTRY(mcck_int_handler)
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mvc __LC_RETURN_MCCK_PSW(16),__PT_PSW(%r11) # move return PSW
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tm __LC_RETURN_MCCK_PSW+1,0x01 # returning to user ?
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jno 0f
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BPON
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stpt __LC_EXIT_TIMER
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mvc __VDSO_ECTG_BASE(16,%r14),__LC_EXIT_TIMER
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0: lmg %r11,%r15,__PT_R11(%r11)
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@ -543,6 +543,7 @@ static struct kset *ipl_kset;
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static void __ipl_run(void *unused)
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{
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__bpon();
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diag308(DIAG308_LOAD_CLEAR, NULL);
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if (MACHINE_IS_VM)
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__cpcmd("IPL", NULL, 0, NULL);
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@ -319,6 +319,7 @@ static void pcpu_delegate(struct pcpu *pcpu, void (*func)(void *),
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mem_assign_absolute(lc->restart_fn, (unsigned long) func);
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mem_assign_absolute(lc->restart_data, (unsigned long) data);
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mem_assign_absolute(lc->restart_source, source_cpu);
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__bpon();
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asm volatile(
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"0: sigp 0,%0,%2 # sigp restart to target cpu\n"
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" brc 2,0b # busy, try again\n"
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@ -903,6 +904,7 @@ void __cpu_die(unsigned int cpu)
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void __noreturn cpu_die(void)
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{
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idle_task_exit();
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__bpon();
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pcpu_sigp_retry(pcpu_devices + smp_processor_id(), SIGP_STOP, 0);
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for (;;) ;
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}
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