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>
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 5d87eda..e6d7550 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -159,6 +159,34 @@
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 @@
*/
nop 0
+ENTRY(__bpon)
+ .globl __bpon
+ BPON
+ br %r14
+
/*
* Scheduler resume function, called by switch_to
* gpr2 = (task_struct *) prev
@@ -226,8 +259,11 @@
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 @@
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 @@
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(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(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 @@
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(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 @@
.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 @@
*/
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 @@
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)
