Re: [PATCH] KVM: x86: fix kvmclock breakage from timers branch merge

Paolo Bonzini
2014-09-04T19:42:44Z

Il 04/09/2014 21:15, Paolo Bonzini ha scritto:
> Il 04/09/2014 20:16, Chris J Arges ha scritto:
>>> + boot_ns = timespec_to_ns(&tk->total_sleep_time)
>>> + + tk->wall_to_monotonic.tv_sec * (u64)NSEC_PER_SEC
>>> + + tk->wall_to_monotonic.tv_nsec
>>> + + tk->xtime_sec * (u64)NSEC_PER_SEC;
>
> So this means that the above 3.16-based code is not the same as
>
> boot_ns = ktime_to_ns(ktime_add(tk->tkr.base_mono, tk->offs_boot));
>
> in 3.17. Everything else in the patch you tested is the same as the
> code that is in 3.17, so that's a start.
>
> Paolo
>

Based on commit 02cba1598a2a3b689e79ad6dad2532521f638271 we have:

offs_real - offs_boot = wall_to_monotonic + total_sleep_time

The patch I posted this morning separates tk->xtime_sec out of boot_ns, so
all that is missing should be a change in boot_ns from base_mono + offs_boot
to offs_real - offs_boot.

Chris, can you try this patch on top of the previous one:

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 92493e10937c..811eecc43fe8 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1031,7 +1031,7 @@ static void update_pvclock_gtod(struct timekeeper *tk)
struct pvclock_gtod_data *vdata = &pvclock_gtod_data;
u64 boot_ns;

- boot_ns = ktime_to_ns(ktime_add(tk->tkr.base_mono, tk->offs_boot));
+ boot_ns = ktime_to_ns(ktime_sub(tk->offs_real, tk->offs_boot));

write_seqcount_begin(&vdata->seq);

If it doesn't work, then commit 02cba1598a2a3b689e79ad6dad2532521f638271
is also broken.

Paolo