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Re: [Xen-devel] Re: [PATCH] xen: drop anti-dependency on X86_VISWS

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] xen: drop anti-dependency on X86_VISWS
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 08 Apr 2011 11:24:20 -0700
Cc: "randy.dunlap@xxxxxxxxxx" <randy.dunlap@xxxxxxxxxx>, Jeremy Fitzhardinge <Jeremy.Fitzhardinge@xxxxxxxxxx>, "eric.dumazet@xxxxxxxxx" <eric.dumazet@xxxxxxxxx>, "konrad.wilk@xxxxxxxxxx" <konrad.wilk@xxxxxxxxxx>, "virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx" <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, "mingo@xxxxxxxxxx" <mingo@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "hpa@xxxxxxxxx" <hpa@xxxxxxxxx>, "tglx@xxxxxxxxxxxxx" <tglx@xxxxxxxxxxxxx>, "mirq-linux@xxxxxxxxxxxx" <mirq-linux@xxxxxxxxxxxx>, "pazke@xxxxxxxxx" <pazke@xxxxxxxxx>, David Miller <davem@xxxxxxxxxxxxx>
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On 04/08/2011 08:42 AM, Jan Beulich wrote:
>>>> On 08.04.11 at 17:25, Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
>> On 04/07/2011 11:38 PM, Ian Campbell wrote:
>>> Is there any downside to this patch (is X86_CMPXCHG in the same sort of
>>> boat?)
>> Only if we don't use cmpxchg in shared memory with other domains or the
>> hypervisor.  (I don't think it will dynamically switch between real and
>> emulated cmpxchg depending on availability.)
> Actually it does - see the "#ifndef CONFIG_X86_CMPXCHG" section
> in asm/cmpxchg_32.h.

Hm, OK.  Still, I'm happiest with that dependency in case someone
knobbles the cpu to exclude cmpxchg and breaks things.

    J

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