[PATCH 08/19] s390: run user space and KVM guests with modified branch prediction

27 Apr 2018

[ 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
---
 arch/s390/include/asm/processor.h   |  3 +++
 arch/s390/include/asm/thread_info.h |  4 +++
 arch/s390/kernel/entry.S            | 51 +++++++++++++++++++++++++++++++++----
 arch/s390/kernel/processor.c        | 18 +++++++++++++
 4 files changed, 71 insertions(+), 5 deletions(-)

diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index 9c442f663fda..0a39cd102c49 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -378,6 +378,9 @@ extern void memcpy_absolute(void *, void *, size_t);
    memcpy_absolute(&(dest), &__tmp, sizeof(__tmp));	\
 } while (0)
+extern int s390_isolate_bp(void);
+extern int s390_isolate_bp_guest(void);
+
 #endif /* __ASSEMBLY__ */
#endif /* __ASM_S390_PROCESSOR_H */
diff --git a/arch/s390/include/asm/thread_info.h b/arch/s390/include/asm/thread_info.h
index 0880a37b6d3b..301b4f70bf31 100644
--- a/arch/s390/include/asm/thread_info.h
+++ b/arch/s390/include/asm/thread_info.h
@@ -60,6 +60,8 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
 #define TIF_GUARDED_STORAGE	4	/* load guarded storage control block */
 #define TIF_PATCH_PENDING	5	/* pending live patching update */
 #define TIF_PGSTE		6	/* New mm's will use 4K page tables */
+#define TIF_ISOLATE_BP		8	/* Run process with isolated BP */
+#define TIF_ISOLATE_BP_GUEST	9	/* Run KVM guests with isolated BP */
#define TIF_31BIT		16	/* 32bit process */
 #define TIF_MEMDIE		17	/* is terminating due to OOM killer */
@@ -80,6 +82,8 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
 #define _TIF_UPROBE		_BITUL(TIF_UPROBE)
 #define _TIF_GUARDED_STORAGE	_BITUL(TIF_GUARDED_STORAGE)
 #define _TIF_PATCH_PENDING	_BITUL(TIF_PATCH_PENDING)
+#define _TIF_ISOLATE_BP		_BITUL(TIF_ISOLATE_BP)
+#define _TIF_ISOLATE_BP_GUEST	_BITUL(TIF_ISOLATE_BP_GUEST)
#define _TIF_31BIT		_BITUL(TIF_31BIT)
 #define _TIF_SINGLE_STEP	_BITUL(TIF_SINGLE_STEP)
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index b1a61b06118a..bb9a6a9808e9 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -106,6 +106,7 @@ _PIF_WORK	= (_PIF_PER_TRAP | _PIF_SYSCALL_RESTART)
    aghi	%r15,-(STACK_FRAME_OVERHEAD + __PT_SIZE)
    j	3f
 1:	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
@@ -186,6 +187,40 @@ _PIF_WORK	= (_PIF_PER_TRAP | _PIF_SYSCALL_RESTART)
    .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:
    /*
@@ -240,9 +275,11 @@ 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
@@ -259,11 +296,12 @@ 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)
 .Lsie_entry:
    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
@@ -324,6 +362,7 @@ ENTRY(system_call)
    la	%r11,STACK_FRAME_OVERHEAD(%r15)	# pointer to pt_regs
 .Lsysc_vtime:
    UPDATE_VTIME %r8,%r9,__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
@@ -362,7 +401,7 @@ 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)
@@ -587,6 +626,7 @@ ENTRY(pgm_check_handler)
    aghi	%r15,-(STACK_FRAME_OVERHEAD + __PT_SIZE)
    j	4f
 2:	UPDATE_VTIME %r14,%r15,__LC_SYNC_ENTER_TIMER
+	BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP
    lg	%r15,__LC_KERNEL_STACK
    lgr	%r14,%r12
    aghi	%r14,__TASK_thread	# pointer to thread_struct
@@ -718,7 +758,7 @@ 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
@@ -1101,7 +1141,7 @@ 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)
@@ -1228,7 +1268,8 @@ cleanup_critical:
    clg     %r9,BASED(.Lsie_crit_mcck_length)
    jh      1f
    oi      __LC_CPU_FLAGS+7, _CIF_MCCK_GUEST
-1:	lg	%r9,__SF_EMPTY(%r15)		# get control block pointer
+1:	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
    larl	%r9,sie_exit			# skip forward to sie_exit
diff --git a/arch/s390/kernel/processor.c b/arch/s390/kernel/processor.c
index 5362fd868d0d..6fe2e1875058 100644
--- a/arch/s390/kernel/processor.c
+++ b/arch/s390/kernel/processor.c
@@ -197,3 +197,21 @@ 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);
-- 
2.13.5

    

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[PATCH 08/19] s390: run user space and KVM guests with modified branch prediction