[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <54AB9FFD.6070309@redhat.com>
Date: Tue, 06 Jan 2015 09:42:37 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/2] x86, vdso, pvclock: Simplify and speed up the vdso
pvclock reader
On 05/01/2015 23:48, Marcelo Tosatti wrote:
>>> > > But there is no guarantee that vCPU-N has updated its pvti when
>>> > > vCPU-M resumes guest instruction execution.
>> >
>> > Still confused. So we can freeze all vCPUs in the host, then update
>> > pvti 1, then resume vCPU 1, then update pvti 0? In that case, we have
>> > a problem, because vCPU 1 can observe pvti 0 mid-update, and KVM
>> > doesn't increment the version pre-update, and we can return completely
>> > bogus results.
> Yes.
But then the getcpu test would fail (1->0). Even if you have an ABA
situation (1->0->1), it's okay because the pvti that is fetched is the
one returned by the first getcpu.
Paolo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists