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authorAndi Kleen <ak@suse.de>2005-09-12 12:49:24 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2005-09-12 13:50:55 -0400
commit083044e63b4d10ebf9afb231bc0d34aec72169b4 (patch)
tree4724a4d993dc1c45830bd8cf39ab5fef70391cd6 /arch/x86_64
parentfe5d5f073eb133b65a8814b48af1722a1ca5aa25 (diff)
[PATCH] x86-64: Remove disable_tsc code in context switch
It only offers extremly dubious security advantages and is not worth the overhead in this critical path. Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'arch/x86_64')
-rw-r--r--arch/x86_64/kernel/process.c29
1 files changed, 0 insertions, 29 deletions
diff --git a/arch/x86_64/kernel/process.c b/arch/x86_64/kernel/process.c
index e9f35c60f8c6..687ed357e685 100644
--- a/arch/x86_64/kernel/process.c
+++ b/arch/x86_64/kernel/process.c
@@ -487,33 +487,6 @@ out:
487} 487}
488 488
489/* 489/*
490 * This function selects if the context switch from prev to next
491 * has to tweak the TSC disable bit in the cr4.
492 */
493static inline void disable_tsc(struct task_struct *prev_p,
494 struct task_struct *next_p)
495{
496 struct thread_info *prev, *next;
497
498 /*
499 * gcc should eliminate the ->thread_info dereference if
500 * has_secure_computing returns 0 at compile time (SECCOMP=n).
501 */
502 prev = prev_p->thread_info;
503 next = next_p->thread_info;
504
505 if (has_secure_computing(prev) || has_secure_computing(next)) {
506 /* slow path here */
507 if (has_secure_computing(prev) &&
508 !has_secure_computing(next)) {
509 write_cr4(read_cr4() & ~X86_CR4_TSD);
510 } else if (!has_secure_computing(prev) &&
511 has_secure_computing(next))
512 write_cr4(read_cr4() | X86_CR4_TSD);
513 }
514}
515
516/*
517 * This special macro can be used to load a debugging register 490 * This special macro can be used to load a debugging register
518 */ 491 */
519#define loaddebug(thread,r) set_debug(thread->debugreg ## r, r) 492#define loaddebug(thread,r) set_debug(thread->debugreg ## r, r)
@@ -631,8 +604,6 @@ struct task_struct *__switch_to(struct task_struct *prev_p, struct task_struct *
631 } 604 }
632 } 605 }
633 606
634 disable_tsc(prev_p, next_p);
635
636 return prev_p; 607 return prev_p;
637} 608}
638 609