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Commit 7d96fd41 authored by Petr Tesarik's avatar Petr Tesarik Committed by Thomas Gleixner
Browse files

x86: move rdtsc_barrier() into the TSC vread method 



The *fence instructions were moved to vsyscall_64.c by commit
cb9e35dc.  But this breaks the
vDSO, because vread methods are also called from there.

Besides, the synchronization might be unnecessary for other
time sources than TSC.

[ Impact: fix potential time warp in VDSO ]

Signed-off-by: default avatarPetr Tesarik <ptesarik@suse.cz>
LKML-Reference: <9d0ea9ea0f866bdc1f4d76831221ae117f11ea67.1243241859.git.ptesarik@suse.cz>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: <stable@kernel.org>
parent cd86a536

arch/x86/kernel/tsc.c

+10 −1
Original line number Original line Diff line number Diff line
@@ -710,7 +710,16 @@ static cycle_t read_tsc(struct clocksource *cs) 
#ifdef CONFIG_X86_64

#ifdef CONFIG_X86_64

static cycle_t __vsyscall_fn vread_tsc(void)

static cycle_t __vsyscall_fn vread_tsc(void)

{

{

	cycle_t ret = (cycle_t)vget_cycles();

	cycle_t ret;



	/*

	 * Surround the RDTSC by barriers, to make sure it's not

	 * speculated to outside the seqlock critical section and

	 * does not cause time warps:

	 */

	rdtsc_barrier();

	ret = (cycle_t)vget_cycles();

	rdtsc_barrier();





	return ret >= __vsyscall_gtod_data.clock.cycle_last ?

	return ret >= __vsyscall_gtod_data.clock.cycle_last ?

		ret : __vsyscall_gtod_data.clock.cycle_last;

		ret : __vsyscall_gtod_data.clock.cycle_last;

arch/x86/kernel/vsyscall_64.c

+0 −8
Original line number Original line Diff line number Diff line
@@ -132,15 +132,7 @@ static __always_inline void do_vgettimeofday(struct timeval * tv) 
			return;

			return;

		}

		}





		/*

		 * Surround the RDTSC by barriers, to make sure it's not

		 * speculated to outside the seqlock critical section and

		 * does not cause time warps:

		 */

		rdtsc_barrier();

		now = vread();

		now = vread();

		rdtsc_barrier();



		base = __vsyscall_gtod_data.clock.cycle_last;

		base = __vsyscall_gtod_data.clock.cycle_last;

		mask = __vsyscall_gtod_data.clock.mask;

		mask = __vsyscall_gtod_data.clock.mask;

		mult = __vsyscall_gtod_data.clock.mult;

		mult = __vsyscall_gtod_data.clock.mult;