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

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Date:	Thu, 04 Sep 2014 21:42:44 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Chris J Arges <chris.j.arges@...onical.com>,
	linux-kernel@...r.kernel.org
CC:	kvm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH] KVM: x86: fix kvmclock breakage from timers branch merge

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
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