search for: ktime_get_boot_n

...t; > > &ka->master_cycle_now); > > > > > > kvm_get_time_and_clockread() gets those values from > > > do_monotonic_boot(), which, barring bugs, should cause > > > get_kvmclock_ns() to return exactly the same thing as > > > ktime_get_boot_ns() + ka->kvmclock_offset, albeit in a rather > > > roundabout manner. > > > > > > So what am I missing? Is there actually something wrong with my patch? > > > > For the bug mentioned in the comment not to happen, you must only read > > TSC and add it...

...t; > > &ka->master_cycle_now); > > > > > > kvm_get_time_and_clockread() gets those values from > > > do_monotonic_boot(), which, barring bugs, should cause > > > get_kvmclock_ns() to return exactly the same thing as > > > ktime_get_boot_ns() + ka->kvmclock_offset, albeit in a rather > > > roundabout manner. > > > > > > So what am I missing? Is there actually something wrong with my patch? > > > > For the bug mentioned in the comment not to happen, you must only read > > TSC and add it...

...( > &ka->master_kernel_ns, > &ka->master_cycle_now); > > kvm_get_time_and_clockread() gets those values from > do_monotonic_boot(), which, barring bugs, should cause > get_kvmclock_ns() to return exactly the same thing as > ktime_get_boot_ns() + ka->kvmclock_offset, albeit in a rather > roundabout manner. > > So what am I missing? Is there actually something wrong with my patch? For the bug mentioned in the comment not to happen, you must only read TSC and add it as offset to (TSC value, time-of-day data). Its more tha...

...( > &ka->master_kernel_ns, > &ka->master_cycle_now); > > kvm_get_time_and_clockread() gets those values from > do_monotonic_boot(), which, barring bugs, should cause > get_kvmclock_ns() to return exactly the same thing as > ktime_get_boot_ns() + ka->kvmclock_offset, albeit in a rather > roundabout manner. > > So what am I missing? Is there actually something wrong with my patch? For the bug mentioned in the comment not to happen, you must only read TSC and add it as offset to (TSC value, time-of-day data). Its more tha...

...t of reading two > > different clocks (one is CLOCK_MONOTONIC and the other is TSC), > > and using those two clocks to as a "base + offset". > > > > As the comment explains, if you do that, can't guarantee monotonicity. > > > > > actually calling ktime_get_boot_ns() could be non-monotonic > > > with respect to the kvmclock timing. But get_kvmclock_ns() isn't used > > > for VM timing as such -- it's used for the IOCTL interfaces for > > > updating the time offset. So can you explain how my patch is > > > incorrec...

...t of reading two > > different clocks (one is CLOCK_MONOTONIC and the other is TSC), > > and using those two clocks to as a "base + offset". > > > > As the comment explains, if you do that, can't guarantee monotonicity. > > > > > actually calling ktime_get_boot_ns() could be non-monotonic > > > with respect to the kvmclock timing. But get_kvmclock_ns() isn't used > > > for VM timing as such -- it's used for the IOCTL interfaces for > > > updating the time offset. So can you explain how my patch is > > > incorrec...

...mp;ka->master_kernel_ns, > > &ka->master_cycle_now); > > > > kvm_get_time_and_clockread() gets those values from > > do_monotonic_boot(), which, barring bugs, should cause > > get_kvmclock_ns() to return exactly the same thing as > > ktime_get_boot_ns() + ka->kvmclock_offset, albeit in a rather > > roundabout manner. > > > > So what am I missing? Is there actually something wrong with my patch? > > For the bug mentioned in the comment not to happen, you must only read > TSC and add it as offset to (TSC value, time...

...s a bug. Its just a side effect of reading two > different clocks (one is CLOCK_MONOTONIC and the other is TSC), > and using those two clocks to as a "base + offset". > > As the comment explains, if you do that, can't guarantee monotonicity. > > > actually calling ktime_get_boot_ns() could be non-monotonic > > with respect to the kvmclock timing. But get_kvmclock_ns() isn't used > > for VM timing as such -- it's used for the IOCTL interfaces for > > updating the time offset. So can you explain how my patch is > > incorrect? > > ktime_g...

...; different clocks (one is CLOCK_MONOTONIC and the other is TSC), > > > and using those two clocks to as a "base + offset". > > > > > > As the comment explains, if you do that, can't guarantee monotonicity. > > > > > > > actually calling ktime_get_boot_ns() could be non-monotonic > > > > with respect to the kvmclock timing. But get_kvmclock_ns() isn't used > > > > for VM timing as such -- it's used for the IOCTL interfaces for > > > > updating the time offset. So can you explain how my patch is > &gt...

On Thu, Oct 04, 2018 at 03:15:32PM -0700, Andy Lutomirski wrote: > For better or for worse, I'm trying to understand this code. So far, > I've come up with this patch: > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/vdso-tglx&id=14fd71e12b1c4492a06f368f75041f263e6862bf > > Is it correct, or am I missing some subtlety? The master

On Thu, Oct 04, 2018 at 03:15:32PM -0700, Andy Lutomirski wrote: > For better or for worse, I'm trying to understand this code. So far, > I've come up with this patch: > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/vdso-tglx&id=14fd71e12b1c4492a06f368f75041f263e6862bf > > Is it correct, or am I missing some subtlety? The master

...source = kvm_get_time_and_clockread( &ka->master_kernel_ns, &ka->master_cycle_now); kvm_get_time_and_clockread() gets those values from do_monotonic_boot(), which, barring bugs, should cause get_kvmclock_ns() to return exactly the same thing as ktime_get_boot_ns() + ka->kvmclock_offset, albeit in a rather roundabout manner. So what am I missing? Is there actually something wrong with my patch? > > See the following comment on x86.c: I read that comment, and it's not obvious to me how it's related.

> On Oct 4, 2018, at 12:31 PM, Peter Zijlstra <peterz at infradead.org> wrote: > > On Thu, Oct 04, 2018 at 07:00:45AM -0700, Andy Lutomirski wrote: >>> On Oct 4, 2018, at 1:11 AM, Peter Zijlstra <peterz at infradead.org> wrote: >>> >>>> On Thu, Oct 04, 2018 at 09:54:45AM +0200, Vitaly Kuznetsov wrote: >>>> I was hoping to hear this

> On Oct 4, 2018, at 12:31 PM, Peter Zijlstra <peterz at infradead.org> wrote: > > On Thu, Oct 04, 2018 at 07:00:45AM -0700, Andy Lutomirski wrote: >>> On Oct 4, 2018, at 1:11 AM, Peter Zijlstra <peterz at infradead.org> wrote: >>> >>>> On Thu, Oct 04, 2018 at 09:54:45AM +0200, Vitaly Kuznetsov wrote: >>>> I was hoping to hear this