Re: [Xen-devel] [PATCH 2/8] x86/head: Refactor 32-bit pgtable setup

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 10/14/2016 02:31 PM, hpa@xxxxxxxxx wrote:
> On October 14, 2016 11:05:12 AM PDT, Boris Ostrovsky 
> <boris.ostrovsky@xxxxxxxxxx> wrote:
>> From: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
>>
>> The new Xen PVH entry point requires page tables to be setup by the
>> kernel since it is entered with paging disabled.
>>
>> Pull the common code out of head_32.S and into pgtable_32.S so that
>> setup_pgtable_32 can be invoked from both the new Xen entry point and
>> the existing startup_32 code.
>>
> And why does it need a separate entry point as opposed to the plain one?

One reason is that we need to prepare boot_params before jumping to
startup_{32|64}.

When the guest is loaded (always in 32-bit mode) the only thing we have
is a pointer to Xen-specific datastructure. The early PVH code will
prepare zeropage based on that structure and then jump to regular
startup_*() code.

-boris

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