From: Paolo Bonzini <pbonzini@redhat.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
kvm list <kvm@vger.kernel.org>, Gleb Natapov <gleb@kernel.org>,
Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: [RFC 2/2] x86, vdso, pvclock: Simplify and speed up the vdso pvclock reader
Date: Wed, 07 Jan 2015 10:00:28 +0100 [thread overview]
Message-ID: <54ACF5AC.4030700@redhat.com> (raw)
In-Reply-To: <CALCETrXGGV9R_4Knz_0LTaz3X2PS1KJDdBfq_RHAVquKdUjrYQ@mail.gmail.com>
On 07/01/2015 08:18, Andy Lutomirski wrote:
>>> >> Thus far, I've been told unambiguously that a guest can't observe pvti
>>> >> while it's being written, and I think you're now telling me that this
>>> >> isn't true and that a guest *can* observe pvti while it's being
>>> >> written while the low bit of the version field is not set. If so,
>>> >> this is rather strongly incompatible with the spec in the KVM docs.
>> >
>> > Where am I saying that?
> I thought the conclusion from what you and Marcelo pointed out about
> the code was that, once the first vCPU updated its pvti, it could
> start running guest code while the other vCPUs are still updating
> pvti, so its guest code can observe the other vCPUs mid-update.
Ah, in that sense you're right. However, each VCPU cannot observe _its
own_ pvti entry while it's being written (no matter what's in the low
bit of the version field).
Paolo
next prev parent reply other threads:[~2015-01-07 9:00 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-23 0:39 [RFC 0/2] x86, vdso, pvclock: Cleanups and speedups Andy Lutomirski
2014-12-23 0:39 ` [RFC 1/2] x86, vdso: Use asm volatile in __getcpu Andy Lutomirski
2014-12-23 0:39 ` Andy Lutomirski
2014-12-23 0:39 ` [RFC 2/2] x86, vdso, pvclock: Simplify and speed up the vdso pvclock reader Andy Lutomirski
2014-12-23 10:28 ` David Vrabel
2014-12-23 10:28 ` [Xen-devel] " David Vrabel
2014-12-23 15:14 ` Boris Ostrovsky
2014-12-23 15:14 ` [Xen-devel] " Boris Ostrovsky
2014-12-23 15:14 ` Paolo Bonzini
2014-12-23 15:14 ` [Xen-devel] " Paolo Bonzini
2014-12-23 15:25 ` Boris Ostrovsky
2014-12-23 15:25 ` Boris Ostrovsky
2014-12-24 21:30 ` David Matlack
2014-12-24 21:30 ` David Matlack
2014-12-24 21:43 ` Andy Lutomirski
2014-12-24 21:43 ` Andy Lutomirski
2015-01-05 15:25 ` Marcelo Tosatti
2015-01-05 15:25 ` Marcelo Tosatti
2015-01-05 18:56 ` Andy Lutomirski
2015-01-05 18:56 ` Andy Lutomirski
2015-01-05 19:17 ` Marcelo Tosatti
2015-01-05 19:17 ` Marcelo Tosatti
2015-01-05 22:38 ` Andy Lutomirski
2015-01-05 22:48 ` Marcelo Tosatti
2015-01-05 22:53 ` Andy Lutomirski
2015-01-05 22:53 ` Andy Lutomirski
2015-01-06 8:42 ` Paolo Bonzini
2015-01-06 8:42 ` Paolo Bonzini
2015-01-06 12:01 ` Paolo Bonzini
2015-01-06 16:56 ` Andy Lutomirski
2015-01-06 16:56 ` Andy Lutomirski
2015-01-06 18:13 ` Marcelo Tosatti
2015-01-06 18:26 ` Andy Lutomirski
2015-01-06 18:26 ` Andy Lutomirski
2015-01-06 18:45 ` Marcelo Tosatti
2015-01-06 19:49 ` Andy Lutomirski
2015-01-06 19:49 ` Andy Lutomirski
2015-01-06 20:20 ` Marcelo Tosatti
2015-01-06 20:20 ` Marcelo Tosatti
2015-01-06 21:54 ` Andy Lutomirski
2015-01-06 21:54 ` Andy Lutomirski
2015-01-08 22:31 ` Marcelo Tosatti
2015-01-08 22:31 ` Marcelo Tosatti
2015-01-08 22:43 ` Andy Lutomirski
2015-01-08 22:43 ` Andy Lutomirski
2015-02-26 22:46 ` Andy Lutomirski
2015-02-26 22:46 ` Andy Lutomirski
2015-01-06 18:45 ` Marcelo Tosatti
2015-01-07 5:41 ` Paolo Bonzini
2015-01-07 5:41 ` Paolo Bonzini
2015-01-06 18:13 ` Marcelo Tosatti
2015-01-07 5:38 ` Paolo Bonzini
2015-01-07 7:18 ` Andy Lutomirski
2015-01-07 7:18 ` Andy Lutomirski
2015-01-07 9:00 ` Paolo Bonzini [this message]
2015-01-07 9:00 ` Paolo Bonzini
2015-01-07 14:45 ` Marcelo Tosatti
2015-01-07 14:45 ` Marcelo Tosatti
2015-01-07 5:38 ` Paolo Bonzini
2015-01-05 22:48 ` Marcelo Tosatti
2015-01-05 22:38 ` Andy Lutomirski
2015-01-06 8:39 ` Paolo Bonzini
2015-01-06 8:39 ` Paolo Bonzini
2015-01-05 22:23 ` Paolo Bonzini
2015-01-05 22:23 ` Paolo Bonzini
2015-01-06 14:35 ` Konrad Rzeszutek Wilk
2015-01-06 14:35 ` [Xen-devel] " Konrad Rzeszutek Wilk
2015-01-08 12:51 ` David Vrabel
2015-01-08 12:51 ` [Xen-devel] " David Vrabel
2014-12-23 0:39 ` Andy Lutomirski
2014-12-23 7:21 ` [RFC 0/2] x86, vdso, pvclock: Cleanups and speedups Paolo Bonzini
2014-12-23 8:16 ` Andy Lutomirski
2014-12-23 8:30 ` Paolo Bonzini
2014-12-23 8:30 ` Paolo Bonzini
2014-12-23 8:16 ` Andy Lutomirski
2014-12-23 7:21 ` Paolo Bonzini
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