s390: run user space and KVM guests with modified branch prediction

[ Upstream commit 6b73044b2b0081ee3dd1cd6eaab7dee552601efb ]

Define TIF_ISOLATE_BP and TIF_ISOLATE_BP_GUEST and add the necessary
plumbing in entry.S to be able to run user space and KVM guests with
limited branch prediction.

To switch a user space process to limited branch prediction the
s390_isolate_bp() function has to be call, and to run a vCPU of a KVM
guest associated with the current task with limited branch prediction
call s390_isolate_bp_guest().

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 63 insertions, 4 deletions

diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index bfcf04de5808..0dd787aabac7 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -105,6 +105,7 @@ _PIF_WORK	= (_PIF_PER_TRAP)
 	j	3f
 1:	LAST_BREAK %r14
 	UPDATE_VTIME %r14,%r15,\timer
+	BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP
 2:	lg	%r15,__LC_ASYNC_STACK	# load async stack
 3:	la	%r11,STACK_FRAME_OVERHEAD(%r15)
 	.endm
@@ -191,6 +192,40 @@ _PIF_WORK	= (_PIF_PER_TRAP)
 	.popsection
 	.endm
 
+	.macro BPENTER tif_ptr,tif_mask
+	.pushsection .altinstr_replacement, "ax"
+662:	.word	0xc004, 0x0000, 0x0000	# 6 byte nop
+	.word	0xc004, 0x0000, 0x0000	# 6 byte nop
+	.popsection
+664:	TSTMSK	\tif_ptr,\tif_mask
+	jz	. + 8
+	.long	0xb2e8d000
+	.pushsection .altinstructions, "a"
+	.long 664b - .
+	.long 662b - .
+	.word 82
+	.byte 12
+	.byte 12
+	.popsection
+	.endm
+
+	.macro BPEXIT tif_ptr,tif_mask
+	TSTMSK	\tif_ptr,\tif_mask
+	.pushsection .altinstr_replacement, "ax"
+662:	jnz	. + 8
+	.long	0xb2e8d000
+	.popsection
+664:	jz	. + 8
+	.long	0xb2e8c000
+	.pushsection .altinstructions, "a"
+	.long 664b - .
+	.long 662b - .
+	.word 82
+	.byte 8
+	.byte 8
+	.popsection
+	.endm
+
 	.section .kprobes.text, "ax"
 .Ldummy:
 	/*
@@ -248,9 +283,11 @@ ENTRY(__switch_to)
  */
 ENTRY(sie64a)
 	stmg	%r6,%r14,__SF_GPRS(%r15)	# save kernel registers
+	lg	%r12,__LC_CURRENT
 	stg	%r2,__SF_EMPTY(%r15)		# save control block pointer
 	stg	%r3,__SF_EMPTY+8(%r15)		# save guest register save area
 	xc	__SF_EMPTY+16(8,%r15),__SF_EMPTY+16(%r15) # reason code = 0
+	mvc	__SF_EMPTY+24(8,%r15),__TI_flags(%r12) # copy thread flags
 	TSTMSK	__LC_CPU_FLAGS,_CIF_FPU		# load guest fp/vx registers ?
 	jno	.Lsie_load_guest_gprs
 	brasl	%r14,load_fpu_regs		# load guest fp/vx regs
@@ -267,10 +304,11 @@ ENTRY(sie64a)
 	jnz	.Lsie_skip
 	TSTMSK	__LC_CPU_FLAGS,_CIF_FPU
 	jo	.Lsie_skip			# exit if fp/vx regs changed
-	BPON
+	BPEXIT	__SF_EMPTY+24(%r15),(_TIF_ISOLATE_BP|_TIF_ISOLATE_BP_GUEST)
 	sie	0(%r14)
 .Lsie_exit:
 	BPOFF
+	BPENTER	__SF_EMPTY+24(%r15),(_TIF_ISOLATE_BP|_TIF_ISOLATE_BP_GUEST)
 .Lsie_skip:
 	ni	__SIE_PROG0C+3(%r14),0xfe	# no longer in SIE
 	lctlg	%c1,%c1,__LC_USER_ASCE		# load primary asce
@@ -332,6 +370,7 @@ ENTRY(system_call)
 	LAST_BREAK %r13
 .Lsysc_vtime:
 	UPDATE_VTIME %r10,%r13,__LC_SYNC_ENTER_TIMER
+	BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP
 	stmg	%r0,%r7,__PT_R0(%r11)
 	# clear user controlled register to prevent speculative use
 	xgr	%r0,%r0
@@ -369,7 +408,7 @@ ENTRY(system_call)
 	jnz	.Lsysc_work			# check for work
 	TSTMSK	__LC_CPU_FLAGS,_CIF_WORK
 	jnz	.Lsysc_work
-	BPON
+	BPEXIT	__TI_flags(%r12),_TIF_ISOLATE_BP
 .Lsysc_restore:
 	lg	%r14,__LC_VDSO_PER_CPU
 	lmg	%r0,%r10,__PT_R0(%r11)
@@ -555,6 +594,7 @@ ENTRY(pgm_check_handler)
 	j	3f
 2:	LAST_BREAK %r14
 	UPDATE_VTIME %r14,%r15,__LC_SYNC_ENTER_TIMER
+	BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP
 	lg	%r15,__LC_KERNEL_STACK
 	lg	%r14,__TI_task(%r12)
 	aghi	%r14,__TASK_thread	# pointer to thread_struct
@@ -683,7 +723,7 @@ ENTRY(io_int_handler)
 	mvc	__LC_RETURN_PSW(16),__PT_PSW(%r11)
 	tm	__PT_PSW+1(%r11),0x01	# returning to user ?
 	jno	.Lio_exit_kernel
-	BPON
+	BPEXIT	__TI_flags(%r12),_TIF_ISOLATE_BP
 .Lio_exit_timer:
 	stpt	__LC_EXIT_TIMER
 	mvc	__VDSO_ECTG_BASE(16,%r14),__LC_EXIT_TIMER
@@ -1044,7 +1084,7 @@ 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
+	BPEXIT	__TI_flags(%r12),_TIF_ISOLATE_BP
 	stpt	__LC_EXIT_TIMER
 	mvc	__VDSO_ECTG_BASE(16,%r14),__LC_EXIT_TIMER
 0:	lmg	%r11,%r15,__PT_R11(%r11)
@@ -1165,6 +1205,7 @@ cleanup_critical:
 	.quad	.Lsie_done
 
 .Lcleanup_sie:
+	BPENTER __SF_EMPTY+24(%r15),(_TIF_ISOLATE_BP|_TIF_ISOLATE_BP_GUEST)
 	lg	%r9,__SF_EMPTY(%r15)		# get control block pointer
 	ni	__SIE_PROG0C+3(%r9),0xfe	# no longer in SIE
 	lctlg	%c1,%c1,__LC_USER_ASCE		# load primary asce
diff --git a/arch/s390/kernel/processor.c b/arch/s390/kernel/processor.c
index 81d0808085e6..d856263fd768 100644
--- a/arch/s390/kernel/processor.c
+++ b/arch/s390/kernel/processor.c
@@ -179,3 +179,21 @@ const struct seq_operations cpuinfo_op = {
 	.stop	= c_stop,
 	.show	= show_cpuinfo,
 };
+
+int s390_isolate_bp(void)
+{
+	if (!test_facility(82))
+		return -EOPNOTSUPP;
+	set_thread_flag(TIF_ISOLATE_BP);
+	return 0;
+}
+EXPORT_SYMBOL(s390_isolate_bp);
+
+int s390_isolate_bp_guest(void)
+{
+	if (!test_facility(82))
+		return -EOPNOTSUPP;
+	set_thread_flag(TIF_ISOLATE_BP_GUEST);
+	return 0;
+}
+EXPORT_SYMBOL(s390_isolate_bp_guest);