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Re: [Xen-devel] x86-64's paging_init()

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] x86-64's paging_init()
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Fri, 01 Sep 2006 16:58:05 +0100
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On 1/9/06 4:49 pm, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx> wrote:

>>> Correct. I suggest either a clean BUG_ON() in virt_to_xen_l2e(), or
>>> allocate-and-map the new l2 in that same function (but raises question of
>>> how to test the new code path).
>> Why in virt_to_xen_l2e()? We likely wouldn't make it there on a system
>> this big, due to earlier memory corruption.
> Why? The memory is only discovered and mapped after the e820 map is parsed.
> The mapping occurs via map_pages_to_xen(). That function discovers the l2e
> by using virt_to_xen_l2e(). So I think it ought to work.
> You can test it out by doing a map_pages_to_xen() call on an area of virtual
> address space that currently has no l2e. Should crash now, and work with the
> modified virt_to_xen_l2e().

Actually virt_to_xen_l2e() already allocates pagetables on demand, it turns
out. So I think there is no issue here that needs fixing.

 -- Keir

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