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

[Julien Grall <julien.grall@xxxxxxx>]

Hi Wei,

On 10/09/18 10:42, Wei Chen (Arm Technology China) wrote:
> > -----Original Message-----
> > From: Julien Grall <julien.grall@xxxxxxxxxx>
> > Sent: 2018年9月10日 17:35
> > 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 10:27, Wei Chen (Arm Technology China) wrote:
> > > > -----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.
> > To be honest, I think it is also wrong to apply this for KVM. KVM is
> > just the hypervisor part and will not care about the memory layout.
> >
> > You then have the monitor (e.g KVMtools, QEMU...) that will define the
> > layout. Your layout here is *only* for QEMU KVM. So you will end up
> > implementing n times KVM support (one for each monitor).
> Yes, you're right, it's for QEMU/KVM only.
>
> > Anyway, for Xen you will have to discover the memory layout at boot.
> > This is something you might be able to use for KVM later on.
> Emm, I will place the memory layout discovery in my TODO list.
TBH, you have most of it :). The only code that seem to be platform 
dependent is the creation of the page-table in the assembly code.
Cheers,

--
Julien Grall

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