Messages in this thread Patch in this message | | | Date | Tue, 30 Jun 2009 17:23:35 -0700 | From | Greg KH <> | Subject | [patch 046/108] x86: move rdtsc_barrier() into the TSC vread method |
| |
2.6.30-stable review patch. If anyone has any objections, please let us know.
------------------
From: Petr Tesarik <ptesarik@suse.cz>
commit 7d96fd41cadc55f4e00231c8c71b8e25c779f122 upstream.
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 <ptesarik@suse.cz> LKML-Reference: <9d0ea9ea0f866bdc1f4d76831221ae117f11ea67.1243241859.git.ptesarik@suse.cz> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- arch/x86/kernel/tsc.c | 11 ++++++++++- arch/x86/kernel/vsyscall_64.c | 8 -------- 2 files changed, 10 insertions(+), 9 deletions(-)
--- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -710,7 +710,16 @@ static cycle_t read_tsc(struct clocksour #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; --- a/arch/x86/kernel/vsyscall_64.c +++ b/arch/x86/kernel/vsyscall_64.c @@ -132,15 +132,7 @@ static __always_inline void do_vgettimeo 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(); - rdtsc_barrier(); - base = __vsyscall_gtod_data.clock.cycle_last; mask = __vsyscall_gtod_data.clock.mask; mult = __vsyscall_gtod_data.clock.mult;
| |