Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit d768bd89 authored by Martin Schwidefsky's avatar Martin Schwidefsky
Browse files

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: default avatarCornelia Huck <cohuck@redhat.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent cf148998

arch/s390/Kconfig

+17 −0
Original line number Diff line number Diff line
@@ -540,6 +540,23 @@ config ARCH_RANDOM 


	  If unsure, say Y.



config KERNEL_NOBP

	def_bool n

	prompt "Enable modified branch prediction for the kernel by default"

	help

	  If this option is selected the kernel will switch to a modified

	  branch prediction mode if the firmware interface is available.

	  The modified branch prediction mode improves the behaviour in

	  regard to speculative execution.



	  With the option enabled the kernel parameter "nobp=0" or "nospec"

	  can be used to run the kernel in the normal branch prediction mode.



	  With the option disabled the modified branch prediction mode is

	  enabled with the "nobp=1" kernel parameter.



	  If unsure, say N.



endmenu



menu "Memory setup"

arch/s390/include/asm/processor.h

+1 −0
Original line number Diff line number Diff line
@@ -91,6 +91,7 @@ void cpu_detect_mhz_feature(void); 
extern const struct seq_operations cpuinfo_op;

extern int sysctl_ieee_emulation_warnings;

extern void execve_tail(void);

extern void __bpon(void);



/*

 * User space process size: 2GB for 31 bit, 4TB or 8PT for 64 bit.

arch/s390/kernel/alternative.c

+23 −0
Original line number Diff line number Diff line
@@ -15,6 +15,29 @@ static int __init disable_alternative_instructions(char *str) 


early_param("noaltinstr", disable_alternative_instructions);



static int __init nobp_setup_early(char *str)

{

	bool enabled;

	int rc;



	rc = kstrtobool(str, &enabled);

	if (rc)

		return rc;

	if (enabled && test_facility(82))

		__set_facility(82, S390_lowcore.alt_stfle_fac_list);

	else

		__clear_facility(82, S390_lowcore.alt_stfle_fac_list);

	return 0;

}

early_param("nobp", nobp_setup_early);



static int __init nospec_setup_early(char *str)

{

	__clear_facility(82, S390_lowcore.alt_stfle_fac_list);

	return 0;

}

early_param("nospec", nospec_setup_early);



struct brcl_insn {

	u16 opc;

	s32 disp;

arch/s390/kernel/early.c

+2 −0
Original line number Diff line number Diff line
@@ -196,6 +196,8 @@ static noinline __init void setup_facility_list(void) 
	memcpy(S390_lowcore.alt_stfle_fac_list,

	       S390_lowcore.stfle_fac_list,

	       sizeof(S390_lowcore.alt_stfle_fac_list));

	if (!IS_ENABLED(CONFIG_KERNEL_NOBP))

		__clear_facility(82, S390_lowcore.alt_stfle_fac_list);

}



static __init void detect_diag9c(void)

arch/s390/kernel/entry.S

+48 −0
Original line number Diff line number Diff line
@@ -159,6 +159,34 @@ _PIF_WORK = (_PIF_PER_TRAP | _PIF_SYSCALL_RESTART) 
		tm	off+\addr, \mask

	.endm



	.macro BPOFF

	.pushsection .altinstr_replacement, "ax"

660:	.long	0xb2e8c000

	.popsection

661:	.long	0x47000000

	.pushsection .altinstructions, "a"

	.long 661b - .

	.long 660b - .

	.word 82

	.byte 4

	.byte 4

	.popsection

	.endm



	.macro BPON

	.pushsection .altinstr_replacement, "ax"

662:	.long	0xb2e8d000

	.popsection

663:	.long	0x47000000

	.pushsection .altinstructions, "a"

	.long 663b - .

	.long 662b - .

	.word 82

	.byte 4

	.byte 4

	.popsection

	.endm



	.section .kprobes.text, "ax"

.Ldummy:

	/*
@@ -171,6 +199,11 @@ _PIF_WORK = (_PIF_PER_TRAP | _PIF_SYSCALL_RESTART) 
	 */

	nop	0



ENTRY(__bpon)

	.globl __bpon

	BPON

	br	%r14



/*

 * Scheduler resume function, called by switch_to

 *  gpr2 = (task_struct *) prev
@@ -226,8 +259,11 @@ ENTRY(sie64a) 
	jnz	.Lsie_skip

	TSTMSK	__LC_CPU_FLAGS,_CIF_FPU

	jo	.Lsie_skip			# exit if fp/vx regs changed

	BPON

.Lsie_entry:

	sie	0(%r14)

.Lsie_exit:

	BPOFF

.Lsie_skip:

	ni	__SIE_PROG0C+3(%r14),0xfe	# no longer in SIE

	lctlg	%c1,%c1,__LC_USER_ASCE		# load primary asce
@@ -279,6 +315,7 @@ ENTRY(system_call) 
	stpt	__LC_SYNC_ENTER_TIMER

.Lsysc_stmg:

	stmg	%r8,%r15,__LC_SAVE_AREA_SYNC

	BPOFF

	lg	%r12,__LC_CURRENT

	lghi	%r13,__TASK_thread

	lghi	%r14,_PIF_SYSCALL
@@ -325,6 +362,7 @@ ENTRY(system_call) 
	jnz	.Lsysc_work			# check for work

	TSTMSK	__LC_CPU_FLAGS,_CIF_WORK

	jnz	.Lsysc_work

	BPON

.Lsysc_restore:

	lg	%r14,__LC_VDSO_PER_CPU

	lmg	%r0,%r10,__PT_R0(%r11)
@@ -530,6 +568,7 @@ ENTRY(kernel_thread_starter) 


ENTRY(pgm_check_handler)

	stpt	__LC_SYNC_ENTER_TIMER

	BPOFF

	stmg	%r8,%r15,__LC_SAVE_AREA_SYNC

	lg	%r10,__LC_LAST_BREAK

	lg	%r12,__LC_CURRENT
@@ -637,6 +676,7 @@ ENTRY(pgm_check_handler) 
ENTRY(io_int_handler)

	STCK	__LC_INT_CLOCK

	stpt	__LC_ASYNC_ENTER_TIMER

	BPOFF

	stmg	%r8,%r15,__LC_SAVE_AREA_ASYNC

	lg	%r12,__LC_CURRENT

	larl	%r13,cleanup_critical
@@ -687,9 +727,13 @@ ENTRY(io_int_handler) 
	lg	%r14,__LC_VDSO_PER_CPU

	lmg	%r0,%r10,__PT_R0(%r11)

	mvc	__LC_RETURN_PSW(16),__PT_PSW(%r11)

	tm	__PT_PSW+1(%r11),0x01	# returning to user ?

	jno	.Lio_exit_kernel

	BPON

.Lio_exit_timer:

	stpt	__LC_EXIT_TIMER

	mvc	__VDSO_ECTG_BASE(16,%r14),__LC_EXIT_TIMER

.Lio_exit_kernel:

	lmg	%r11,%r15,__PT_R11(%r11)

	lpswe	__LC_RETURN_PSW

.Lio_done:
@@ -860,6 +904,7 @@ ENTRY(io_int_handler) 
ENTRY(ext_int_handler)

	STCK	__LC_INT_CLOCK

	stpt	__LC_ASYNC_ENTER_TIMER

	BPOFF

	stmg	%r8,%r15,__LC_SAVE_AREA_ASYNC

	lg	%r12,__LC_CURRENT

	larl	%r13,cleanup_critical
@@ -908,6 +953,7 @@ ENTRY(psw_idle) 
.Lpsw_idle_stcctm:

#endif

	oi	__LC_CPU_FLAGS+7,_CIF_ENABLED_WAIT

	BPON

	STCK	__CLOCK_IDLE_ENTER(%r2)

	stpt	__TIMER_IDLE_ENTER(%r2)

.Lpsw_idle_lpsw:
@@ -1008,6 +1054,7 @@ load_fpu_regs: 
 */

ENTRY(mcck_int_handler)

	STCK	__LC_MCCK_CLOCK

	BPOFF

	la	%r1,4095		# validate r1

	spt	__LC_CPU_TIMER_SAVE_AREA-4095(%r1)	# validate cpu timer

	sckc	__LC_CLOCK_COMPARATOR			# validate comparator
@@ -1118,6 +1165,7 @@ ENTRY(mcck_int_handler) 
	mvc	__LC_RETURN_MCCK_PSW(16),__PT_PSW(%r11) # move return PSW

	tm	__LC_RETURN_MCCK_PSW+1,0x01 # returning to user ?

	jno	0f

	BPON

	stpt	__LC_EXIT_TIMER

	mvc	__VDSO_ECTG_BASE(16,%r14),__LC_EXIT_TIMER

0:	lmg	%r11,%r15,__PT_R11(%r11)