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Re: [Xen-devel] [PATCH 0/5] x86: properly propagate errors to hypercall

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 0/5] x86: properly propagate errors to hypercall callee
From: Keir Fraser <keir.xen@xxxxxxxxx>
Date: Fri, 11 Mar 2011 09:45:07 +0000
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] [PATCH 0/5] x86: properly propagate errors to hypercall callee
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On 11/03/2011 09:25, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:

>>>> On 09.03.11 at 12:07, Keir Fraser <keir.xen@xxxxxxxxx> wrote:
>> It seems unfortunate to propagate this to guests. Perhaps we should be
>> making a memory pool for Xen's 1:1 mappings, big enough to allow a 4kB
>> mapping of every page of RAM in the system, and allocate/free pagetables to
>> that pool? The overhead of this would be no more than 0.2% of system memory,
>> which seems reasonable to avoid an error case that is surely hard for a
>> guest to react to or fix.
> Before starting to look into eventual Linux side changes - do you
> then have plans to go that pool route (which would make guest
> side recovery attempts pointless)?

Not really. I was thinking about having a Linux-style mempool for making
allocations more likely to succeed, but it's all a bit ugly really. It'll be
interesting to see what you can do Linux-side, and whether it can pass
muster for the Linux maintainers. You might at least be able to make the io
remappings from device drivers failable (and maybe they are already).

 -- Keir

> Jan

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