Re: [Xen-users] ARM: Xen on Vexpress

[Jeenu Viswambharan <Jeenu.Viswambharan@xxxxxxx>]

On Wed, Jun 11, 2014 at 16:10:46, Ian Campbell wrote:
> On Wed, 2014-06-11 at 16:02 +0100, Jeenu Viswambharan wrote:
> > > > Xen is now launching DOM0. But next issue I'm now facing is that
> > > > Linux refusing to run when loaded at 0xa0008000 - it panics and
> > > > complains about failing to allocate memory in
> > > > mm/memblock.c:memblock_alloc_base().  FWIW, I've built the
> > > > kernel v3.14 with vexpress_defconfig and enabled Xen and highmem
> > > > support.  The kernel however is happy to boot when loaded at
> > > > 0x80008000 (without Xen). The same with Xen though, the kernel
> > > > reports 'uncompression error'.
> > > >
> > > > It's little to do with Xen, but are there any other options
> > > > required to be enabled in the DOM0 Kernel to run from
> > > > 0xa0008000?
> > >
> > > Your kernel needs to be relocatable. I'm not 100% which option
> > > that is (perhaps CONFIG_ARM_PATCH_PHYS_VIRT) but if you build a
> > > multiplatform kernel (CONFIG_ARCH_MULTIPLATFORM) it certainly will
> > > be.
> >
> > Just found out that both of the configs are enabled in my build, and
> > I've no idea what's going on.
> >
> > Like I said, when loaded at 0xa0008000, the kernel didn't boot
> > neither on bare metal nor Xen. But at 0x80008000, the kernel was
> > happy to boot bare metal but not with Xen. Does Xen care where the
> > kernel is, as long as the kernel is happy to execute from wherever
> > it's loaded?
>
> The kernel wants to be loaded within 128M of the start of RAM. Does
> 0xa0008000 meet that? What is loading the kernel there -- I don't
> think Xen will (it knows about the 128MB thing). How much RAM does
> your vexpress have? Is 0xa0008000 even in RAM on a vexpress? I thought
> it had up to 1GB at 0x60000000-0xa0000000.

The TC2 has 1GB RAM from 0x80000000 to 0xc0000000. The instructions on
the Wiki tells u-boot to load it at 0xa0008000 and modifies the DTB
accordingly.

> And just to be clear we are talking about the load address of the
> kernel within the dom0 IPA space, aren't we? Not the host address
> where the kernel is loaded to be passed to Xen (it doesn't matter what
> that is really).

I think, upon guest entry, the PC will be at 0xa0008000, making both IPA
and PA same [1]. Is that what you were asking?

> Can you post your boot logs, perhaps they will give me a clue.

I only have

  (XEN) DOM0: Uncompressing Linux... done, booting the kernel.

at the console. The rest is in the log buffer which I can view through
the debugger. I've attached the best I could muster.

--
Jeenu

[1] 
http://wiki.xenproject.org/wiki/Xen_ARM_with_Virtualization_Extensions/Vexpress#Set_up_U-Boot_to_boot_via_PXE




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