Re: [PATCH v2 6/9] xen: arm: rewrite start of day page table and cpu bring up

[Tim Deegan <tim@xen.org>]

At 13:59 +0100 on 26 Sep (1380203962), Ian Campbell wrote:
> From cd92dd41a1bb8de3cf145f90f89e645a5c9049bf Mon Sep 17 00:00:00 2001
> From: Ian Campbell <ian.campbell@citrix.com>
> Date: Thu, 29 Aug 2013 16:25:00 +0100
> Subject: [PATCH] xen: arm: rewrite start of day page table and cpu bring up
> 
> This is unfortunately a rather large monolithic patch.
> 
> Rather than bringing up all CPUs in lockstep as we setup paging and relocate
> Xen instead create a simplified set of dedicated boot time pagetables.
> 
> This allows secondary CPUs to remain powered down or in the firmware until we
> actually want to enable them. The bringup is now done later on in C and can be
> driven by DT etc. I have included code for the vexpress platform, but other
> platforms will need to be added.
> 
> The mechanism for deciding how to bring up a CPU differs between arm32 and
> arm64. On arm32 it is essentially a per-platform property, with the exception
> of PSCI which can be implemented globally (but isn't here). On arm64 there is a
> per-cpu property in the device tree.
> 
> Secondary CPUs are brought up directly into the relocated Xen image, instead of
> relying on being able to launch on the unrelocated Xen and hoping that it
> hasn't been clobbered.
> 
> As part of this change drop support for switching from secure mode to NS HYP as
> well as the early CPU kick. Xen now requires that it is launched in NS HYP
> mode and that firmware configure things such that secondary CPUs can be woken
> up by a primarly CPU in HYP mode. This may require fixes to bootloaders or the
> use of a boot wrapper.
> 
> The changes done here (re)exposed an issue with relocating Xen and the compiler
> spilling values to the stack between the copy and the actual switch to the
> relocaed copy of Xen in setup_pagetables. Therefore switch to doing the copy
> and switch in a single asm function where we can control precisely what gets
> spilled to the stack etc.
> 
> Since we now have a separate set of boot pagetables it is much easier to build
> the real Xen pagetables inplace before relocating rather than the more complex
> approach of rewriting the pagetables in the relocated copy before switching.
> 
> This will also enable Xen to be loaded above the 4GB boundary on 64-bit.
> 
> Still TODO:
>   - integrate with Julien's "Dissociate logical and hardware CPU ID"
>   - cpu initialisation for other platforms
> 
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

Acked-by: Tim Deegan <tim@xen.org>