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From: Marcelo Tosatti <mtosatti@redhat.com>
To: Alexander Graf <agraf@suse.de>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org
Subject: Re: [Qemu-devel] [PATCH] kvmclock: Ensure time in migration never goes backward
Date: Wed, 7 May 2014 22:33:25 -0300	[thread overview]
Message-ID: <20140508013325.GA5474@amt.cnet> (raw)
In-Reply-To: <1399297882-3444-1-git-send-email-agraf@suse.de>

On Mon, May 05, 2014 at 03:51:22PM +0200, Alexander Graf wrote:
> When we migrate we ask the kernel about its current belief on what the guest
> time would be. However, I've seen cases where the kvmclock guest structure
> indicates a time more recent than the kvm returned time.
> 
> To make sure we never go backwards, calculate what the guest would have seen
> as time at the point of migration and use that value instead of the kernel
> returned one when it's more recent.
> 
> While this doesn't fix the underlying issue that the kernel's view of time
> is skewed, it allows us to safely migrate guests even from sources that are
> known broken.
> 
> Signed-off-by: Alexander Graf <agraf@suse.de>

OK Alexander better move this logic to the kernel, in KVM_GET_CLOCK.

Otherwise every user of KVM_GET_CLOCK would have to apply the
workaround.

  parent reply	other threads:[~2014-05-08  1:38 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-05-05 13:51 [Qemu-devel] [PATCH] kvmclock: Ensure time in migration never goes backward Alexander Graf
2014-05-05 17:46 ` Marcin Gibuła
2014-05-05 18:05   ` Alexander Graf
2014-05-05 18:26     ` Marcin Gibuła
2014-05-05 23:27       ` Marcelo Tosatti
2014-05-05 23:31         ` Marcelo Tosatti
2014-05-06  8:07           ` Marcin Gibuła
2014-05-06  7:11         ` Alexander Graf
2014-05-06  7:37         ` Marcin Gibuła
2014-05-05 23:23 ` Marcelo Tosatti
2014-05-05 23:31   ` Marcelo Tosatti
2014-05-06  7:18     ` Alexander Graf
2014-05-06 19:54       ` Marcin Gibuła
2014-05-07 23:23         ` Marcelo Tosatti
2014-05-07 23:21       ` Marcelo Tosatti
2014-05-07 23:29         ` Alexander Graf
2014-05-06  7:16   ` Alexander Graf
2014-05-07 10:04     ` Nick Thomas
2014-05-08  1:33 ` Marcelo Tosatti [this message]
2014-05-08  7:21   ` Alexander Graf
2014-05-09  2:28     ` Marcelo Tosatti
2014-05-09 11:53       ` Paolo Bonzini
2014-05-12 20:26         ` Alexander Graf
2014-05-14  7:26           ` Marcelo Tosatti
2014-05-14  6:47         ` Marcelo Tosatti

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