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[Xen-devel] RE: The memory type of non-RAM address is WB by default?

To: 'Keir Fraser' <keir.fraser@xxxxxxxxxxxxx>
Subject: [Xen-devel] RE: The memory type of non-RAM address is WB by default?
From: "Cui, Dexuan" <dexuan.cui@xxxxxxxxx>
Date: Thu, 23 Oct 2008 18:24:57 +0800
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Cc: "Su, Disheng" <disheng.su@xxxxxxxxx>, "'xen-devel@xxxxxxxxxxxxxxxxxxx'" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: The memory type of non-RAM address is WB by default?
Keir Fraser wrote:
> Well, one approach would be not to warn! :-)
>
> Seriously: for anything which is not guest RAM, the host should
> really know best what memory type it should be mapped as (probably UC
> or WC). Hence why mess around validating a guest-requested memory
> type?
This method looks good. I'll try to make a patch.

> The alternative is to give guests a shedload more MTRR ranges. This
> is kind of clunky and will also slow down the MTRR-range search which
> Xen currently does when working out guest effective memory type.  But
>  it does have the advantage of letting us have default type as UC,
Maybe this method looks not so appealing. :-)

> I guess is the default type on just about every real machine in
> the world?
I'm not sure, maybe it's platform-dependent?

Thanks,
-- Dexuan

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