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Thomas Gleixner d8bb6f4c16 x86: tsc prevent time going backwards 
We already catch most of the TSC problems by sanity checks, but there
is a subtle bug which has been in the code forever. This can cause
time jumps in the range of hours.

This was reported in:
     http://lkml.org/lkml/2007/8/23/96
and
     http://lkml.org/lkml/2008/3/31/23

I was able to reproduce the problem with a gettimeofday loop test on a
dual core and a quad core machine which both have sychronized
TSCs. The TSCs seems not to be perfectly in sync though, but the
kernel is not able to detect the slight delta in the sync check. Still
there exists an extremly small window where this delta can be observed
with a real big time jump. So far I was only able to reproduce this
with the vsyscall gettimeofday implementation, but in theory this
might be observable with the syscall based version as well.

CPU 0 updates the clock source variables under xtime/vyscall lock and
CPU1, where the TSC is slighty behind CPU0, is reading the time right
after the seqlock was unlocked.

The clocksource reference data was updated with the TSC from CPU0 and
the value which is read from TSC on CPU1 is less than the reference
data. This results in a huge delta value due to the unsigned
subtraction of the TSC value and the reference value. This algorithm
can not be changed due to the support of wrapping clock sources like
pm timer.

The huge delta is converted to nanoseconds and added to xtime, which
is then observable by the caller. The next gettimeofday call on CPU1
will show the correct time again as now the TSC has advanced above the
reference value.

To prevent this TSC specific wreckage we need to compare the TSC value
against the reference value and return the latter when it is larger
than the actual TSC value.

I pondered to mark the TSC unstable when the readout is smaller than
the reference value, but this would render an otherwise good and fast
clocksource unusable without a real good reason.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-04-19 19:19:55 +02:00
..
acpi x86: remove pointless comments 2008-04-19 19:19:54 +02:00
cpu x86: remove pointless comments 2008-04-19 19:19:54 +02:00
.gitignore
alternative.c x86: fix test_poke for vmalloced pages 2008-04-17 17:41:29 +02:00
aperture_64.c x86: clean up aperture_64.c 2008-04-17 17:41:19 +02:00
apic_32.c x86: move up & smp variables to setup.c 2008-04-17 17:41:35 +02:00
apic_64.c x86: move up & smp variables to setup.c 2008-04-17 17:41:35 +02:00
apm_32.c x86: switch to proc_create() 2008-04-17 17:40:51 +02:00
asm-offsets_32.c x86: move struct definitions to unifed sigframe.h 2008-04-17 17:40:46 +02:00
asm-offsets_64.c x86: add asm_offset PARAVIRT constants 2008-01-30 13:33:19 +01:00
asm-offsets.c
audit_64.c
bootflag.c x86: coding style cleanup for kernel/bootflag.c 2008-01-30 13:32:31 +01:00
bugs_64.c x86: don't use large pages to map the first 2/4MB of memory 2008-04-17 17:41:30 +02:00
cpuid.c x86: cpuid, msr: use inode mutex instead of big kernel lock 2008-02-04 16:47:59 +01:00
crash_dump_32.c
crash_dump_64.c
crash.c x86: move ipi definitions to mach_ipi.h 2008-04-17 17:41:30 +02:00
doublefault_32.c
ds.c x86: debug Store - call kfree if only we really need it 2008-04-17 17:41:34 +02:00
e820_32.c x86: reserve end-of-conventional-memory to 1MB on 32-bit 2008-04-17 17:40:51 +02:00
e820_64.c x86: e820_64, fix section mismatch warning 2008-04-19 19:19:54 +02:00
early_printk.c x86: coding style fixes to x86/kernel/early_printk.c 2008-04-17 17:40:51 +02:00
early-quirks.c x86: fix section mismatch warning in early-quirks.c 2008-01-30 13:33:37 +01:00
efi_32.c x86: sparse error in efi_32.c 2008-02-19 16:18:28 +01:00
efi_64.c x86: EFI_PAGE_SHIFT fix 2008-04-19 19:19:54 +02:00
efi_stub_32.S
efi_stub_64.S
efi.c x86: EFI_PAGE_SHIFT fix 2008-04-19 19:19:54 +02:00
entry_32.S x86: remove pointless comments 2008-04-19 19:19:54 +02:00
entry_64.S x86: ptrace vs -ENOSYS 2008-04-17 17:41:13 +02:00
genapic_64.c x86: move x86_cpu_to_apicid_init to smpboot.c 2008-04-17 17:41:34 +02:00
genapic_flat_64.c x86: use cpumask_of_cpu() 2008-04-17 17:41:36 +02:00
genx2apic_uv_x.c x86: support for new UV apic 2008-04-17 17:41:33 +02:00
geode_32.c x86: GEODE: MFGPT: Use "just-in-time" detection for the MFGPT timers 2008-02-09 23:24:08 +01:00
head32.c x86: introduce kernel/head32.c 2008-04-17 17:40:49 +02:00
head64.c x86_64: do not reserve ramdisk two times 2008-04-19 19:19:54 +02:00
head_32.S x86: remove pointless comments 2008-04-19 19:19:54 +02:00
head_64.S x86: move suspend wakeup code to C 2008-04-17 17:41:37 +02:00
hpet.c x86: revert assign IRQs to hpet timer 2008-04-04 18:36:49 +02:00
i386_ksyms_32.c Generic semaphore implementation 2008-04-17 10:42:34 -04:00
i387.c x86: clean up i387.c 2008-04-17 17:40:57 +02:00
i8237.c
i8253.c x86: pit_clockevent can be static 2008-02-13 16:20:35 +01:00
i8259_32.c x86: i8259A: remove redundant irq_descinitialization 2008-02-19 16:18:34 +01:00
i8259_64.c x86: provide a native_init_IRQ function on 64-bit 2008-01-30 13:33:19 +01:00
init_task.c x86: delay the export removal of init_mm 2008-02-29 18:55:42 +01:00
io_apic_32.c x86: remove unnecessary tmp local variable 2008-04-17 17:41:36 +02:00
io_apic_64.c x86: use cpumask_of_cpu() 2008-04-17 17:41:36 +02:00
io_delay.c x86: add dmi quirk for io_delay 2008-03-26 22:23:40 +01:00
ioport.c x86: refactor ioport unification 2008-01-30 13:33:10 +01:00
ipi.c x86: create ipi.c 2008-04-17 17:40:56 +02:00
irq_32.c x86: replace remaining __FUNCTION__ occurances 2008-04-17 17:40:57 +02:00
irq_64.c
k8.c
kdebugfs.c x86 boot : export boot_params via debugfs for debugging 2008-01-30 13:32:51 +01:00
kgdb.c x86: KGDB build fix 2008-04-19 19:19:54 +02:00
kprobes.c x86: replace most VM86 flags with flags from processor-flags.h 2008-04-17 17:41:33 +02:00
ldt.c x86: cleanup - eliminate numbers in LDT allocation code 2008-02-04 16:48:03 +01:00
machine_kexec_32.c vmcoreinfo: fix the configuration dependencies 2008-02-07 08:42:25 -08:00
machine_kexec_64.c vmcoreinfo: add the symbol "phys_base" 2008-04-02 15:28:19 -07:00
Makefile Merge git://git.kernel.org/pub/scm/linux/kernel/git/mingo/linux-2.6-kgdb 2008-04-18 08:37:01 -07:00
mca_32.c x86: coding style fixes to arch/x86/kernel/mca_32.c 2008-04-17 17:40:49 +02:00
mfgpt_32.c x86: GEODE: add missing module.h include 2008-03-26 22:23:40 +01:00
microcode.c x86: microcode: show results on success too 2008-04-17 17:41:32 +02:00
module_32.c
module_64.c
mpparse.c x86: print out buggy mptable 2008-04-17 17:41:36 +02:00
msr.c x86: coding style fixes to arch/x86/kernel/msr.c 2008-04-17 17:40:50 +02:00
nmi_32.c ftrace: add notrace annotations for NMI routines 2008-04-19 19:19:55 +02:00
nmi_64.c ftrace: add notrace annotations for NMI routines 2008-04-19 19:19:55 +02:00
numaq_32.c x86: convert TSC disabling to generic cpuid disable bitmap 2008-01-30 13:33:20 +01:00
paravirt_patch_32.c
paravirt_patch_64.c x86: add stringify header 2008-01-30 13:33:19 +01:00
paravirt.c x86: paravirt_ops: don't steal memory resources in paravirt_disable_iospace 2008-04-17 17:41:33 +02:00
pci-calgary_64.c iommu sg: x86: convert calgary IOMMU to use the IOMMU helper 2008-02-05 09:44:11 -08:00
pci-dma_32.c
pci-dma_64.c x86 iommu: add more documentation 2008-04-17 17:40:59 +02:00
pci-gart_64.c x86, agpgart: scary messages are fortunately obsolete 2008-04-04 18:36:46 +02:00
pci-nommu_64.c
pci-swiotlb_64.c
pcspeaker.c
pmtimer_64.c
process_32.c x86: implement prctl PR_GET_TSC and PR_SET_TSC 2008-04-19 19:19:55 +02:00
process_64.c x86: implement prctl PR_GET_TSC and PR_SET_TSC 2008-04-19 19:19:55 +02:00
ptrace.c x86: regparm(3) is mandatory, no need to annotate 2008-04-17 17:40:45 +02:00
quirks.c x86: hpet clock enable quirk on nVidia nForce 430 2008-03-21 17:06:15 +01:00
reboot_fixups_32.c x86: add the RDC machine specific reboot fixup 2008-01-30 13:33:36 +01:00
reboot.c x86: use cpu_online() 2008-04-17 17:41:36 +02:00
relocate_kernel_32.S x86: relocate_kernel - use predefined macroses for page attributes 2008-04-17 17:41:29 +02:00
relocate_kernel_64.S x86: relocate_kernel - use predefined macroses for page attributes 2008-04-17 17:41:29 +02:00
rtc.c x86: fix cmos read and write to not use inb_p and outb_p 2008-04-17 17:40:47 +02:00
scx200_32.c x86: fix sparse warning in kernel/scx200_32.c 2008-01-31 22:05:45 +01:00
setup64.c x86: fix exec mappings comments 2008-04-19 19:19:55 +02:00
setup_32.c x86: move suspend wakeup code to C 2008-04-17 17:41:37 +02:00
setup_64.c x86_64: do not reserve ramdisk two times 2008-04-19 19:19:54 +02:00
setup.c x86: move up & smp variables to setup.c 2008-04-17 17:41:35 +02:00
sigframe.h x86: move struct definitions to unifed sigframe.h 2008-04-17 17:40:46 +02:00
signal_32.c x86: replace most VM86 flags with flags from processor-flags.h 2008-04-17 17:41:33 +02:00
signal_64.c x86: remove DEBUG_SIG 2008-04-17 17:40:57 +02:00
smp.c x86: move ipi definitions to mach_ipi.h 2008-04-17 17:41:30 +02:00
smpboot.c x86: standalone trampoline code 2008-04-17 17:41:37 +02:00
smpcommon_32.c x86: create smpcommon.c 2008-04-17 17:40:55 +02:00
smpcommon.c x86: create smpcommon.c 2008-04-17 17:40:55 +02:00
srat_32.c x86: replace remaining __FUNCTION__ occurances 2008-04-17 17:40:57 +02:00
stacktrace.c x86: don't save unreliable stack trace entries 2008-02-26 12:55:58 +01:00
step.c x86: prevent unconditional writes to DebugCtl MSR 2008-04-17 17:40:58 +02:00
summit_32.c x86: move mp_bus_id_to_node to numa.c 2008-04-17 17:40:59 +02:00
sys_i386_32.c
sys_x86_64.c
syscall_64.c x86: coding style fixes to arch/x86/kernel/syscall_64.c 2008-04-17 17:40:48 +02:00
syscall_table_32.S timerfd: wire the new timerfd API to the x86 family 2008-02-05 09:44:07 -08:00
tce_64.c
test_nx.c x86: Explicitly include required header files. 2008-04-17 17:41:15 +02:00
test_rodata.c x86: include proper prototypes for rodata_test 2008-02-14 23:30:20 +01:00
time_32.c
time_64.c time: fix typo in comments 2008-02-08 09:22:29 -08:00
tlb_32.c x86: create tlb files 2008-04-17 17:40:56 +02:00
tlb_64.c x86: move ipi definitions to mach_ipi.h 2008-04-17 17:41:30 +02:00
tls.c asmlinkage_protect replaces prevent_tail_call 2008-04-10 17:28:26 -07:00
tls.h
topology.c x86: fix section mismatch warning in topology.c:arch_register_cpu 2008-02-19 16:18:30 +01:00
trampoline_32.S x86: remove misleading comments in trampoline_*.S 2008-02-04 16:48:01 +01:00
trampoline_64.S x86: move suspend wakeup code to C 2008-04-17 17:41:37 +02:00
trampoline.c x86: standalone trampoline code 2008-04-17 17:41:37 +02:00
traps_32.c ftrace: add notrace annotations for NMI routines 2008-04-19 19:19:55 +02:00
traps_64.c ftrace: add notrace annotations for NMI routines 2008-04-19 19:19:55 +02:00
tsc_32.c x86: tsc prevent time going backwards 2008-04-19 19:19:55 +02:00
tsc_64.c x86: tsc prevent time going backwards 2008-04-19 19:19:55 +02:00
tsc_sync.c x86: add warning to check_tsc_warp() 2008-01-30 13:33:24 +01:00
verify_cpu_64.S
vm86_32.c x86: replace most VM86 flags with flags from processor-flags.h 2008-04-17 17:41:33 +02:00
vmi_32.c x86: VMI fix 2008-02-04 16:47:54 +01:00
vmiclock_32.c x86: isolate PIC/PIT in/out calls 2008-01-30 13:33:14 +01:00
vmlinux_32.lds.S x86: use ELF section to list CPU vendor specific code 2008-04-17 17:40:47 +02:00
vmlinux_64.lds.S x86: use ELF section to list CPU vendor specific code 2008-04-17 17:40:47 +02:00
vmlinux.lds.S
vsmp_64.c x86: clean up vSMP detection 2008-04-17 17:41:29 +02:00
vsyscall_64.c x86: restore vsyscall64 prochandler 2008-02-29 18:55:39 +01:00
x8664_ksyms_64.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/x86/linux-2.6-x86 2008-04-18 08:25:51 -07:00