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Re: [Xen-devel] [PATCH] nestedhvm: ASID emulation

To: Christoph Egger <Christoph.Egger@xxxxxxx>
Subject: Re: [Xen-devel] [PATCH] nestedhvm: ASID emulation
From: Keir Fraser <keir.xen@xxxxxxxxx>
Date: Thu, 14 Apr 2011 11:28:54 +0100
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Thread-topic: [Xen-devel] [PATCH] nestedhvm: ASID emulation
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On 14/04/2011 10:26, "Christoph Egger" <Christoph.Egger@xxxxxxx> wrote:

>> What if nv_n2asid wast last assigned on a previous generation, but nv_n1asid
>> was assigned from the current generation? Then you'd have next_asid>
>> nv_n2asid, but nv_n2asid is stale.
> When the generation changes, next_asid is set back to 1 and the hw TLB
> flushed.
> If next_asid is larger than nv_n2asid then it is reused and this is ok
> since the hw TLB got flushed. It is just important that nv_n1asid never
> gets the same hw ASID assigned and that is what the do { } while loop
> ensures.

What if some other vcpu's nv_n1asid or nv_n2asid got assigned the same HW
asid in this generation as this vcpu's (now stale, as it's from a previous
generation's) nv_n2asid? This PCPU can be interleaving execution of other
HVM VCPUs after all.

 -- Keir

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