s390: remove all code using the access register mode

The vdso code for the getcpu() and the clock_gettime() call use the access
register mode to access the per-CPU vdso data page with the current code.

An alternative to the complicated AR mode is to use the secondary space
mode. This makes the vdso faster and quite a bit simpler. The downside is
that the uaccess code has to be changed quite a bit.

Which instructions are used depends on the machine and what kind of uaccess
operation is requested. The instruction dictates which ASCE value needs
to be loaded into %cr1 and %cr7.

The different cases:

* User copy with MVCOS for z10 and newer machines
  The MVCOS instruction can copy between the primary space (aka user) and
  the home space (aka kernel) directly. For set_fs(KERNEL_DS) the kernel
  ASCE is loaded into %cr1. For set_fs(USER_DS) the user space is already
  loaded in %cr1.

* User copy with MVCP/MVCS for older machines
  To be able to execute the MVCP/MVCS instructions the kernel needs to
  switch to primary mode. The control register %cr1 has to be set to the
  kernel ASCE and %cr7 to either the kernel ASCE or the user ASCE dependent
  on set_fs(KERNEL_DS) vs set_fs(USER_DS).

* Data access in the user address space for strnlen / futex
  To use "normal" instruction with data from the user address space the
  secondary space mode is used. The kernel needs to switch to primary mode,
  %cr1 has to contain the kernel ASCE and %cr7 either the user ASCE or the
  kernel ASCE, dependent on set_fs.

To load a new value into %cr1 or %cr7 is an expensive operation, the kernel
tries to be lazy about it. E.g. for multiple user copies in a row with
MVCP/MVCS the replacement of the vdso ASCE in %cr7 with the user ASCE is
done only once. On return to user space a CPU bit is checked that loads the
vdso ASCE again.

To enable and disable the data access via the secondary space two new
functions are added, enable_sacf_uaccess and disable_sacf_uaccess. The fact
that a context is in secondary space uaccess mode is stored in the
mm_segment_t value for the task. The code of an interrupt may use set_fs
as long as it returns to the previous state it got with get_fs with another
call to set_fs. The code in finish_arch_post_lock_switch simply has to do a
set_fs with the current mm_segment_t value for the task.

For CPUs with MVCOS:

CPU running in                        | %cr1 ASCE | %cr7 ASCE |
--------------------------------------|-----------|-----------|
user space                            |  user     |  vdso     |
kernel, USER_DS, normal-mode          |  user     |  vdso     |
kernel, USER_DS, normal-mode, lazy    |  user     |  user     |
kernel, USER_DS, sacf-mode            |  kernel   |  user     |
kernel, KERNEL_DS, normal-mode        |  kernel   |  vdso     |
kernel, KERNEL_DS, normal-mode, lazy  |  kernel   |  kernel   |
kernel, KERNEL_DS, sacf-mode          |  kernel   |  kernel   |

For CPUs without MVCOS:

CPU running in                        | %cr1 ASCE | %cr7 ASCE |
--------------------------------------|-----------|-----------|
user space                            |  user     |  vdso     |
kernel, USER_DS, normal-mode          |  user     |  vdso     |
kernel, USER_DS, normal-mode lazy     |  kernel   |  user     |
kernel, USER_DS, sacf-mode            |  kernel   |  user     |
kernel, KERNEL_DS, normal-mode        |  kernel   |  vdso     |
kernel, KERNEL_DS, normal-mode, lazy  |  kernel   |  kernel   |
kernel, KERNEL_DS, sacf-mode          |  kernel   |  kernel   |

The lines with "lazy" refer to the state after a copy via the secondary
space with a delayed reload of %cr1 and %cr7.

There are three hardware address spaces that can cause a DAT exception,
primary, secondary and home space. The exception can be related to
four different fault types: user space fault, vdso fault, kernel fault,
and the gmap faults.

Dependent on the set_fs state and normal vs. sacf mode there are a number
of fault combinations:

1) user address space fault via the primary ASCE
2) gmap address space fault via the primary ASCE
3) kernel address space fault via the primary ASCE for machines with
   MVCOS and set_fs(KERNEL_DS)
4) vdso address space faults via the secondary ASCE with an invalid
   address while running in secondary space in problem state
5) user address space fault via the secondary ASCE for user-copy
   based on the secondary space mode, e.g. futex_ops or strnlen_user
6) kernel address space fault via the secondary ASCE for user-copy
   with secondary space mode with set_fs(KERNEL_DS)
7) kernel address space fault via the primary ASCE for user-copy
   with secondary space mode with set_fs(USER_DS) on machines without
   MVCOS.
8) kernel address space fault via the home space ASCE

Replace user_space_fault() with a new function get_fault_type() that
can distinguish all four different fault types.

With these changes the futex atomic ops from the kernel and the
strnlen_user will get a little bit slower, as well as the old style
uaccess with MVCP/MVCS. All user accesses based on MVCOS will be as
fast as before. On the positive side, the user space vdso code is a
lot faster and Linux ceases to use the complicated AR mode.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

5 files changed, 46 insertions, 65 deletions

diff --git a/arch/s390/include/asm/futex.h b/arch/s390/include/asm/futex.h
index 9b5a3469fed9..5e97a4353147 100644
--- a/arch/s390/include/asm/futex.h
+++ b/arch/s390/include/asm/futex.h
@@ -26,9 +26,9 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
 		u32 __user *uaddr)
 {
 	int oldval = 0, newval, ret;
+	mm_segment_t old_fs;
 
-	load_kernel_asce();
-
+	old_fs = enable_sacf_uaccess();
 	pagefault_disable();
 	switch (op) {
 	case FUTEX_OP_SET:
@@ -55,6 +55,7 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
 		ret = -ENOSYS;
 	}
 	pagefault_enable();
+	disable_sacf_uaccess(old_fs);
 
 	if (!ret)
 		*oval = oldval;
@@ -65,9 +66,10 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
 static inline int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 						u32 oldval, u32 newval)
 {
+	mm_segment_t old_fs;
 	int ret;
 
-	load_kernel_asce();
+	old_fs = enable_sacf_uaccess();
 	asm volatile(
 		"   sacf 256\n"
 		"0: cs   %1,%4,0(%5)\n"
@@ -77,6 +79,7 @@ static inline int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 		: "=d" (ret), "+d" (oldval), "=m" (*uaddr)
 		: "0" (-EFAULT), "d" (newval), "a" (uaddr), "m" (*uaddr)
 		: "cc", "memory");
+	disable_sacf_uaccess(old_fs);
 	*uval = oldval;
 	return ret;
 }
diff --git a/arch/s390/include/asm/lowcore.h b/arch/s390/include/asm/lowcore.h
index 9eb36a1592c7..2306fa17f6cd 100644
--- a/arch/s390/include/asm/lowcore.h
+++ b/arch/s390/include/asm/lowcore.h
@@ -115,33 +115,28 @@ struct lowcore {
 	/* Address space pointer. */
 	__u64	kernel_asce;			/* 0x0378 */
 	__u64	user_asce;			/* 0x0380 */
+	__u64	vdso_asce;			/* 0x0388 */
 
 	/*
 	 * The lpp and current_pid fields form a
 	 * 64-bit value that is set as program
 	 * parameter with the LPP instruction.
 	 */
-	__u32	lpp;				/* 0x0388 */
-	__u32	current_pid;			/* 0x038c */
+	__u32	lpp;				/* 0x0390 */
+	__u32	current_pid;			/* 0x0394 */
 
 	/* SMP info area */
-	__u32	cpu_nr;				/* 0x0390 */
-	__u32	softirq_pending;		/* 0x0394 */
-	__u64	percpu_offset;			/* 0x0398 */
-	__u64	vdso_per_cpu_data;		/* 0x03a0 */
-	__u64	machine_flags;			/* 0x03a8 */
-	__u32	preempt_count;			/* 0x03b0 */
-	__u8	pad_0x03b4[0x03b8-0x03b4];	/* 0x03b4 */
-	__u64	gmap;				/* 0x03b8 */
-	__u32	spinlock_lockval;		/* 0x03c0 */
-	__u32	spinlock_index;			/* 0x03c4 */
-	__u32	fpu_flags;			/* 0x03c8 */
-	__u8	pad_0x03cc[0x0400-0x03cc];	/* 0x03cc */
-
-	/* Per cpu primary space access list */
-	__u32	paste[16];			/* 0x0400 */
-
-	__u8	pad_0x04c0[0x0e00-0x0440];	/* 0x0440 */
+	__u32	cpu_nr;				/* 0x0398 */
+	__u32	softirq_pending;		/* 0x039c */
+	__u32	preempt_count;			/* 0x03a0 */
+	__u32	spinlock_lockval;		/* 0x03a4 */
+	__u32	spinlock_index;			/* 0x03a8 */
+	__u32	fpu_flags;			/* 0x03ac */
+	__u64	percpu_offset;			/* 0x03b0 */
+	__u64	vdso_per_cpu_data;		/* 0x03b8 */
+	__u64	machine_flags;			/* 0x03c0 */
+	__u64	gmap;				/* 0x03c8 */
+	__u8	pad_0x03d0[0x0e00-0x03d0];	/* 0x03d0 */
 
 	/*
 	 * 0xe00 contains the address of the IPL Parameter Information
diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
index 43607bb12cc2..6133aa376b7c 100644
--- a/arch/s390/include/asm/mmu_context.h
+++ b/arch/s390/include/asm/mmu_context.h
@@ -71,41 +71,38 @@ static inline int init_new_context(struct task_struct *tsk,
 static inline void set_user_asce(struct mm_struct *mm)
 {
 	S390_lowcore.user_asce = mm->context.asce;
-	if (current->thread.mm_segment.ar4)
-		__ctl_load(S390_lowcore.user_asce, 7, 7);
-	set_cpu_flag(CIF_ASCE_PRIMARY);
+	__ctl_load(S390_lowcore.user_asce, 1, 1);
+	clear_cpu_flag(CIF_ASCE_PRIMARY);
 }
 
 static inline void clear_user_asce(void)
 {
 	S390_lowcore.user_asce = S390_lowcore.kernel_asce;
-
-	__ctl_load(S390_lowcore.user_asce, 1, 1);
-	__ctl_load(S390_lowcore.user_asce, 7, 7);
-}
-
-static inline void load_kernel_asce(void)
-{
-	unsigned long asce;
-
-	__ctl_store(asce, 1, 1);
-	if (asce != S390_lowcore.kernel_asce)
-		__ctl_load(S390_lowcore.kernel_asce, 1, 1);
+	__ctl_load(S390_lowcore.kernel_asce, 1, 1);
 	set_cpu_flag(CIF_ASCE_PRIMARY);
 }
 
+mm_segment_t enable_sacf_uaccess(void);
+void disable_sacf_uaccess(mm_segment_t old_fs);
+
 static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 			     struct task_struct *tsk)
 {
 	int cpu = smp_processor_id();
 
-	S390_lowcore.user_asce = next->context.asce;
 	if (prev == next)
 		return;
+	S390_lowcore.user_asce = next->context.asce;
 	cpumask_set_cpu(cpu, &next->context.cpu_attach_mask);
-	/* Clear old ASCE by loading the kernel ASCE. */
-	__ctl_load(S390_lowcore.kernel_asce, 1, 1);
-	__ctl_load(S390_lowcore.kernel_asce, 7, 7);
+	/* Clear previous user-ASCE from CR1 and CR7 */
+	if (!test_cpu_flag(CIF_ASCE_PRIMARY)) {
+		__ctl_load(S390_lowcore.kernel_asce, 1, 1);
+		set_cpu_flag(CIF_ASCE_PRIMARY);
+	}
+	if (test_cpu_flag(CIF_ASCE_SECONDARY)) {
+		__ctl_load(S390_lowcore.vdso_asce, 7, 7);
+		clear_cpu_flag(CIF_ASCE_SECONDARY);
+	}
 	cpumask_clear_cpu(cpu, &prev->context.cpu_attach_mask);
 }
 
@@ -115,7 +112,6 @@ static inline void finish_arch_post_lock_switch(void)
 	struct task_struct *tsk = current;
 	struct mm_struct *mm = tsk->mm;
 
-	load_kernel_asce();
 	if (mm) {
 		preempt_disable();
 		while (atomic_read(&mm->context.flush_count))
diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index f25bfe888933..709351bce80e 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -109,9 +109,7 @@ extern void execve_tail(void);
 
 #define HAVE_ARCH_PICK_MMAP_LAYOUT
 
-typedef struct {
-        __u32 ar4;
-} mm_segment_t;
+typedef unsigned int mm_segment_t;
 
 /*
  * Thread structure
diff --git a/arch/s390/include/asm/uaccess.h b/arch/s390/include/asm/uaccess.h
index cdd0f0d999e2..ad6b91013a05 100644
--- a/arch/s390/include/asm/uaccess.h
+++ b/arch/s390/include/asm/uaccess.h
@@ -16,7 +16,7 @@
 #include <asm/processor.h>
 #include <asm/ctl_reg.h>
 #include <asm/extable.h>
-
+#include <asm/facility.h>
 
 /*
  * The fs value determines whether argument validity checking should be
@@ -26,27 +26,16 @@
  * For historical reasons, these macros are grossly misnamed.
  */
 
-#define MAKE_MM_SEG(a)  ((mm_segment_t) { (a) })
-
-
-#define KERNEL_DS       MAKE_MM_SEG(0)
-#define USER_DS         MAKE_MM_SEG(1)
+#define KERNEL_DS	(0)
+#define KERNEL_DS_SACF	(1)
+#define USER_DS		(2)
+#define USER_DS_SACF	(3)
 
 #define get_ds()        (KERNEL_DS)
 #define get_fs()        (current->thread.mm_segment)
-#define segment_eq(a,b) ((a).ar4 == (b).ar4)
+#define segment_eq(a,b) (((a) & 2) == ((b) & 2))
 
-static inline void set_fs(mm_segment_t fs)
-{
-	current->thread.mm_segment = fs;
-	if (uaccess_kernel()) {
-		set_cpu_flag(CIF_ASCE_SECONDARY);
-		__ctl_load(S390_lowcore.kernel_asce, 7, 7);
-	} else {
-		clear_cpu_flag(CIF_ASCE_SECONDARY);
-		__ctl_load(S390_lowcore.user_asce, 7, 7);
-	}
-}
+void set_fs(mm_segment_t fs);
 
 static inline int __range_ok(unsigned long addr, unsigned long size)
 {
@@ -95,7 +84,7 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long n);
 
 static inline int __put_user_fn(void *x, void __user *ptr, unsigned long size)
 {
-	unsigned long spec = 0x810000UL;
+	unsigned long spec = 0x010000UL;
 	int rc;
 
 	switch (size) {
@@ -125,7 +114,7 @@ static inline int __put_user_fn(void *x, void __user *ptr, unsigned long size)
 
 static inline int __get_user_fn(void *x, const void __user *ptr, unsigned long size)
 {
-	unsigned long spec = 0x81UL;
+	unsigned long spec = 0x01UL;
 	int rc;
 
 	switch (size) {