s390/vdso: fix getcpu
getcpu reads the required values for cpu and node with two
instructions. This might lead to an inconsistent result if user space
gets preempted and migrated to a different CPU between the two
instructions.
Fix this by using just a single instruction to read both values at
once.
This is currently rather a theoretical bug, since there is no real
NUMA support available (except for NUMA emulation).
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
diff --git a/arch/s390/include/asm/vdso.h b/arch/s390/include/asm/vdso.h
index 169d760..3bcfdeb 100644
--- a/arch/s390/include/asm/vdso.h
+++ b/arch/s390/include/asm/vdso.h
@@ -41,8 +41,17 @@
struct vdso_per_cpu_data {
__u64 ectg_timer_base;
__u64 ectg_user_time;
- __u32 cpu_nr;
- __u32 node_id;
+ /*
+ * Note: node_id and cpu_nr must be at adjacent memory locations.
+ * VDSO userspace must read both values with a single instruction.
+ */
+ union {
+ __u64 getcpu_val;
+ struct {
+ __u32 node_id;
+ __u32 cpu_nr;
+ };
+ };
};
extern struct vdso_data *vdso_data;
diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
index 41ac4ad..ce33406 100644
--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -78,8 +78,7 @@
OFFSET(__VDSO_TS_END, vdso_data, ts_end);
OFFSET(__VDSO_ECTG_BASE, vdso_per_cpu_data, ectg_timer_base);
OFFSET(__VDSO_ECTG_USER, vdso_per_cpu_data, ectg_user_time);
- OFFSET(__VDSO_CPU_NR, vdso_per_cpu_data, cpu_nr);
- OFFSET(__VDSO_NODE_ID, vdso_per_cpu_data, node_id);
+ OFFSET(__VDSO_GETCPU_VAL, vdso_per_cpu_data, getcpu_val);
BLANK();
/* constants used by the vdso */
DEFINE(__CLOCK_REALTIME, CLOCK_REALTIME);
diff --git a/arch/s390/kernel/vdso32/getcpu.S b/arch/s390/kernel/vdso32/getcpu.S
index 25515f3..dc79e16 100644
--- a/arch/s390/kernel/vdso32/getcpu.S
+++ b/arch/s390/kernel/vdso32/getcpu.S
@@ -16,10 +16,8 @@
.type __kernel_getcpu,@function
__kernel_getcpu:
CFI_STARTPROC
- la %r4,0
sacf 256
- l %r5,__VDSO_CPU_NR(%r4)
- l %r4,__VDSO_NODE_ID(%r4)
+ lm %r4,%r5,__VDSO_GETCPU_VAL(%r0)
sacf 0
ltr %r2,%r2
jz 2f
diff --git a/arch/s390/kernel/vdso64/getcpu.S b/arch/s390/kernel/vdso64/getcpu.S
index 2446e9d..3c04f7328 100644
--- a/arch/s390/kernel/vdso64/getcpu.S
+++ b/arch/s390/kernel/vdso64/getcpu.S
@@ -16,10 +16,8 @@
.type __kernel_getcpu,@function
__kernel_getcpu:
CFI_STARTPROC
- la %r4,0
sacf 256
- l %r5,__VDSO_CPU_NR(%r4)
- l %r4,__VDSO_NODE_ID(%r4)
+ lm %r4,%r5,__VDSO_GETCPU_VAL(%r0)
sacf 0
ltgr %r2,%r2
jz 2f
