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Re: [Xen-devel] [PATCH] [pv-ops domU] support MAXSMP

To: "Andrew Jones" <drjones@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] [pv-ops domU] support MAXSMP
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Fri, 18 Dec 2009 10:07:09 +0000
Cc: jeremy@xxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx
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>>> Andrew Jones <drjones@xxxxxxxxxx> 18.12.09 10:31 >>>
>The MAXSMP config option requires CPUMASK_OFFSTACK, which in turn
>requires we init the memory for the maps while we bringing up the cpus.
>MAXSMP also increases NR_CPUS to 4096. This increase in size exposed an
>issue in the argument construction for mulitcalls from
>xen_flush_tlb_others. The args should only need space for the actual
>number of cpus, which with xen is currently only up to 32.

I don't think new code should be making assumptions like this anymore,
since Xen already supports higher numbers (it's merely the tools which
so far don't). You're basically trading a compile time detectable large
value on stack for one that can grow large dynamically (and hence
require quite a bit more effort to debug, should it ever overrun the


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