Commit 5a5525b0 authored by Heiko Carstens's avatar Heiko Carstens Committed by Vasily Gorbik
Browse files

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: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarVasily Gorbik <gor@linux.ibm.com>
parent a2308c11

arch/s390/include/asm/vdso.h

+11 −2
Original line number Diff line number Diff line
@@ -41,8 +41,17 @@ struct vdso_data { 
struct vdso_per_cpu_data {

	__u64 ectg_timer_base;

	__u64 ectg_user_time;

	__u32 cpu_nr;

	/*

	 * 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;

arch/s390/kernel/asm-offsets.c

+1 −2
Original line number Diff line number Diff line
@@ -78,8 +78,7 @@ int main(void) 
	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);

arch/s390/kernel/vdso32/getcpu.S

+1 −3
Original line number Diff line number Diff line
@@ -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

arch/s390/kernel/vdso64/getcpu.S

+1 −3
Original line number Diff line number Diff line
@@ -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

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