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

["Wei Chen (Arm Technology China)" <Wei.Chen@xxxxxxx>]

> -----Original Message-----
> From: Julien Grall <julien.grall@xxxxxxxxxx>
> Sent: 2018年9月10日 17:24
> To: Wei Chen (Arm Technology China) <Wei.Chen@xxxxxxx>; Julien Grall
> <Julien.Grall@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
>
>
>
> 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.
>

Ok, I understand now. I would apply this memory layout for KVM only.

> >
> >> 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.

Ok.

>
> Cheers,
>
> --
> Julien Grall
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