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SubjectRe: [Xen-devel] [PATCH 5/7] xen/p2m: Add logic to revector a P2M tree to use __va leafs.
>>> On 27.07.12 at 13:18, Stefano Stabellini <stefano.stabellini@eu.citrix.com> wrote:
> On Thu, 26 Jul 2012, Konrad Rzeszutek Wilk wrote:
>> 1) All P2M lookups instead of using the __ka address would
>> use the __va address. This means we can safely erase from
>> __ka space the PMD pointers that point to the PFNs for
>> P2M array and be OK.
>> 2). Allocate a new array, copy the existing P2M into it,
>> revector the P2M tree to use that, and return the old
>> P2M to the memory allocate. This has the advantage that
>> it sets the stage for using XEN_ELF_NOTE_INIT_P2M
>> feature. That feature allows us to set the exact virtual
>> address space we want for the P2M - and allows us to
>> boot as initial domain on large machines.
>>
>> So we pick option 2).
>
> 1) looks like a decent option that requires less code.
> Is the problem with 1) that we might want to access the P2M before we
> have __va addresses ready?

AIUI 1) has no easy way of subsequently accommodating support
for XEN_ELF_NOTE_INIT_P2M (where you almost definitely will
want/need to reclaim the originally used VA space - if nothing else,
then for forward compatibility with the rest of the kernel).

Jan



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