linux-kernel - Re: Cleaning up the KVM clock

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Message-ID: <54989FF0.3090300@redhat.com>
Date:	Mon, 22 Dec 2014 23:49:20 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Gleb Natapov <gleb@...nel.org>, kvm list <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Cleaning up the KVM clock



On 22/12/2014 17:03, Andy Lutomirski wrote:
> This is wrong.  The guest *kernel* might not see the intermediate
> state because the kernel (presumably it disabled migration while
> reading pvti), but the guest vdso can't do that and could very easily
> observe pvti while it's being written.

No.  kvm_guest_time_update is called by vcpu_enter_guest, while the vCPU
is not running, so it's entirely atomic from the point of view of the guest.

> I'll send patches for the whole mess, complete with lots of comments,
> after I test them a bit today.

Ok, some comments can certainly help the discussion.

Paolo
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