Re: [Minios-devel] [UNIKRAFT PATCHv4 18/43] plat/include: Define address offsets of boot stack and pagetable

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

On 10.07.2018 08:37, Wei Chen wrote:
> Hi Julien,
>
> > -----Original Message-----
> > From: Julien Grall <julien.grall@xxxxxxx>
> > Sent: 2018年7月9日 18:56
> > To: Wei Chen <Wei.Chen@xxxxxxx>; minios-devel@xxxxxxxxxxxxxxxxxxxx;
> > simon.kuenzer@xxxxxxxxx
> > Cc: Kaly Xin <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> > Subject: Re: [Minios-devel] [UNIKRAFT PATCHv4 18/43] plat/include: Define
> > address offsets of boot stack and pagetable
> >
> > On 09/07/18 11:10, Wei Chen wrote:
> > > Hi Julien,
> > Hi Wei,
> >
> >
> > > > -----Original Message-----
> > > > From: Julien Grall <julien.grall@xxxxxxx>
> > > > Sent: 2018年7月9日 4:19
> > > > To: Wei Chen <Wei.Chen@xxxxxxx>; minios-devel@xxxxxxxxxxxxxxxxxxxx;
> > > > simon.kuenzer@xxxxxxxxx
> > > > Cc: Kaly Xin <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> > > > Subject: Re: [Minios-devel] [UNIKRAFT PATCHv4 18/43] plat/include: Define
> > > > address offsets of boot stack and pagetable
> > > >
> > > > Hi Wei,
> > > >
> > > > On 07/06/2018 10:03 AM, Wei Chen wrote:
> > > > > If we place the boot stack and pagetable in BSS section. These
> > > > > areas are not easy to be reused after changing to newstack. So
> > > > s/newstack/a new stack/ or "the new stack".
> > >
> > > Ok
> > >
> > > > > in Arm64, we want to place the pagetable and boot stack behind
> > > > s/behind/after/
> > > Got it.
> > >
> > > > > the end of image.
> > > > > In this case, once we change to newstack or we have new pagetable,
> > > > > these two areas can be reclaimed very easy.
> > > > I am wondering whether it would be worth to introduce an "init" section.
> > > > This would make easier to reclaim the region and avoid hardcoded offset
> > > > below.
> > > If we have a lot of such init functions or data, it would be good to have
> > > a init section. If not, the freed small init section it's not easy managed.
> > > Because VA and PA is 1:1 mapped.
> > I am not sure to understand how this would be difficult to manage? The
> > region will be few tens KB. This is enough to allocate a lot of structure.
> If this region has tens of KB, I think it's valuable to do this.
> But I think this feature is basic and common, and exceeds this
> series scope. How do you think about it @Simon?
We do not have a best practice yet for this case. Also the other 
platform implementations have the potential to claim such regions back 
(which does not happen yet). It sound to me that we need to introduce an 
API so that we can make use of such regions from generic code (e.g., 
from libukboot when memory allocator is initialized). So, I think it is 
fine if it stays as open point for improvement for ARM64-KVM (as like 
x86-KVM, etc.) for now.
> > Cheers,
> >
> > --
> > Julien Grall
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