From 7d96fd41cadc55f4e00231c8c71b8e25c779f122 Mon Sep 17 00:00:00 2001 From: Petr Tesarik Date: Mon, 25 May 2009 11:02:02 +0200 Subject: x86: move rdtsc_barrier() into the TSC vread method The *fence instructions were moved to vsyscall_64.c by commit cb9e35dce94a1b9c59d46224e8a94377d673e204. 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: Petr Tesarik LKML-Reference: <9d0ea9ea0f866bdc1f4d76831221ae117f11ea67.1243241859.git.ptesarik@suse.cz> Signed-off-by: Thomas Gleixner Cc: --- arch/x86/kernel/tsc.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) (limited to 'arch/x86/kernel/tsc.c') diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index d57de05dc43..cf8611d991e 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -710,7 +710,16 @@ static cycle_t read_tsc(struct clocksource *cs) #ifdef CONFIG_X86_64 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 ? ret : __vsyscall_gtod_data.clock.cycle_last; -- cgit v1.2.3