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Re: [Xen-devel] [PATCH] xen/x86: p2m: Don't initialize slot 0 of the P2M
- To: Julien Grall <julien@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: George Dunlap <george.dunlap@xxxxxxxxxx>
- Date: Mon, 3 Feb 2020 17:10:02 +0000
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- Cc: Wei Liu <wl@xxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
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On 2/3/20 4:58 PM, Julien Grall wrote:
> From: Julien Grall <jgrall@xxxxxxxxxx>
>
> It is not entirely clear why the slot 0 of each p2m should be populated
> with empty page-tables. The commit introducing it 759af8e3800 "[HVM]
> Fix 64-bit HVM domain creation." does not contain meaningful
> explanation except that it was necessary for shadow.
Tim, any ideas here?
> As we don't seem to have a good explanation why this is there, drop the
> code completely.
>
> This was tested by successfully booting a HVM with shadow enabled.
>
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
>
> ---
>
> I don't know for sure if this is going to break a setup. I have tried
> HVM guest with hap={0, 1} without any trouble. I am happy to try more
> setup if you have any in mind.
>
> If this break a setup, then please describe the setup and I will send a
> documentation patch instead.
This is a somewhat risky strategy. Other than code clean-up, is there
any advantage to removing this code at the moment?
-George
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