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[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>
This commit is contained in:
Andi Kleen 2005-09-12 18:49:24 +02:00 committed by Linus Torvalds
parent fe5d5f073e
commit 083044e63b
1 changed files with 0 additions and 29 deletions
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29
arch/x86_64/kernel/process.c
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@ -486,33 +486,6 @@ out:
return err;
}
/*
* This function selects if the context switch from prev to next
* has to tweak the TSC disable bit in the cr4.
*/
static inline void disable_tsc(struct task_struct *prev_p,
struct task_struct *next_p)
{
struct thread_info *prev, *next;
/*
* gcc should eliminate the ->thread_info dereference if
* has_secure_computing returns 0 at compile time (SECCOMP=n).
*/
prev = prev_p->thread_info;
next = next_p->thread_info;
if (has_secure_computing(prev) || has_secure_computing(next)) {
/* slow path here */
if (has_secure_computing(prev) &&
!has_secure_computing(next)) {
write_cr4(read_cr4() & ~X86_CR4_TSD);
} else if (!has_secure_computing(prev) &&
has_secure_computing(next))
write_cr4(read_cr4() | X86_CR4_TSD);
}
}
/*
* This special macro can be used to load a debugging register
*/
@ -631,8 +604,6 @@ struct task_struct *__switch_to(struct task_struct *prev_p, struct task_struct *
}
}
disable_tsc(prev_p, next_p);
return prev_p;
}