Re: [Minios-devel] [UNIKRAFT PATCHv5 15/46] plat/include: Define address offsets of boot stack and pagetable

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 10/09/18 09:18, Wei Chen (Arm Technology China) wrote:
> Hi Julien,
Hi,

> > -----Original Message-----
> > From: Julien Grall <julien.grall@xxxxxxx>
> > Sent: 2018年9月7日 22:45
> > To: Wei Chen (Arm Technology China) <Wei.Chen@xxxxxxx>; Simon Kuenzer
> > <simon.kuenzer@xxxxxxxxx>; minios-devel@xxxxxxxxxxxxxxxxxxxx
> > Cc: Kaly Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>
> > Subject: Re: [Minios-devel] [UNIKRAFT PATCHv5 15/46] plat/include: Define
> > address offsets of boot stack and pagetable
> >
> > Hi,
> >
> > On 09/07/2018 10:36 AM, Wei Chen (Arm Technology China) wrote:
> > > > -----Original Message-----
> > > > From: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>
> > > > Sent: 2018年9月7日 17:29
> > > > To: Wei Chen (Arm Technology China) <Wei.Chen@xxxxxxx>; minios-
> > > > devel@xxxxxxxxxxxxxxxxxxxx
> > > > Cc: Kaly Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> > > > Subject: Re: [Minios-devel] [UNIKRAFT PATCHv5 15/46] plat/include: Define
> > > > address offsets of boot stack and pagetable
> > > >
> > > > On 07.09.2018 07:14, Wei Chen (Arm Technology China) wrote:
> > > > > Hi Simon,
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>
> > > > > > Sent: 2018年9月6日 22:53
> > > > > > To: Wei Chen (Arm Technology China) <Wei.Chen@xxxxxxx>; minios-
> > > > > > devel@xxxxxxxxxxxxxxxxxxxx
> > > > > > Cc: Kaly Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> > > > > > Subject: Re: [Minios-devel] [UNIKRAFT PATCHv5 15/46] plat/include: Define
> > > > > > address offsets of boot stack and pagetable
> > > > > >
> > > > > > Hey Wei,
> > > > > >
> > > > > > These defines for the memory layout are specific for KVM for now, right?
> > > > > > Wouldn't it then make sense to place this files to plat/kvm/include?
> > > > > > Or do you know if this is going to be the same for Xen?
> > > > > I want to use the same memory layout for KVM and Xen. I know that current
> > > > > Code for Xen platform is ported from mini-os. But once, when code for
> > > > > Arm/KVM becomes stable, I want reuse most of the code for these two
> > > > > platforms.
> > > > Okay, sounds reasonable. Could you add this as one sentence in the
> > > > commit message to eplain why you decided to place this to common/?
> > > Ok, I will add similar comment in the commit message.
> > I don't think this memory layout is going to work well with Xen because
> > you can't assume there are free RAM after the kernel image.
> Why I can't assume that? I will design the link script and write the boot
> code, I can tell kernel image how to use the RAM. Anything I had missed?
The memory layout in Xen is not part of the ABI. This give Xen the 
freedom to shuffle the layout between versions if required.
So you can't assume where the kernel will be positioned in memory nor if 
there is any space after.
> > It would be best if you make sure the boot stack and pagetable are
> > contained in BSS but towards the end. You can then free them once you
> > are done with it. This has also the advantage to avoid hardcoding address.
> I remember we had discussed it in previous version about implementing an
> "init section". We may do it in later patches, but not now.
I will answer to this in the linker script thread.

Cheers,

--
Julien Grall

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