Re: [Viryaos-discuss] [ImageBuilder] [PATCH 2/2] uboot-script-gen: Enable direct mapping of statically allocated memory

[Ayan Kumar Halder <ayankuma@xxxxxxx>]

On 23/06/2022 13:05, xenia wrote:
> Hi Ayan!
Hi Xenia,
> On 6/23/22 13:02, Ayan Kumar Halder wrote:
> > (Resending mail, as the previous delivery failed)
> >
> > On 21/06/2022 12:34, Ayan Kumar Halder wrote:
> > > Hi,
> > >
> > > On 19/06/2022 13:43, Xenia Ragiadakou wrote:
> > > > Direct mapping for dom0less VMs is disabled by default in XEN and 
> > > > can be
> > > > enabled through the 'direct-map' property.
> > > > Add a new config parameter DOMU_DIRECT_MAP to be able to enable or 
> > > > disable
> > > > direct mapping, i.e set to 1 for enabling and to 0 for disabling.
> > > > This parameter is optional. Direct mapping is enabled by default 
> > > > for all
> > > > dom0less VMs with static allocation.
> > > >
> > > > The property 'direct-map' is a boolean property. Boolean properties 
> > > > are true
> > > > if present and false if missing.
> > > > Add a new data_type 'bool' in function dt_set() to setup a boolean 
> > > > property.
> > > > Signed-off-by: Xenia Ragiadakou <burzalodowa@xxxxxxxxx>
> > > > ---
> > > >   README.md                |  4 ++++
> > > >   scripts/uboot-script-gen | 18 ++++++++++++++++++
> > > >   2 files changed, 22 insertions(+)
> > > >
> > > > diff --git a/README.md b/README.md
> > > > index c52e4b9..17ff206 100644
> > > > --- a/README.md
> > > > +++ b/README.md
> > > > @@ -168,6 +168,10 @@ Where:
> > > >     if specified, indicates the host physical address regions
> > > >     [baseaddr, baseaddr + size) to be reserved to the VM for static 
> > > > allocation.
> > > >   +- DOMU_DIRECT_MAP[number] can be set to 1 or 0.
> > > > +  If set to 1, the VM is direct mapped. The default is 1.
> > > > +  This is only applicable when DOMU_STATIC_MEM is specified.
> > > Can't we just use $DOMU_STATIC_MEM to set "direct-map" in dts ?
> > >
> > > Is there a valid use-case for static allocation without direct 
> > > mapping ? Sorry, it is not very clear to me.
> Thank you for taking the time to review the patch!
>
> I agree with you that static allocation without direct mapping is not 
> a common configuration, that's why, in the script, direct mapping is 
> enabled by default.
> My reasoning was that, since direct mapping is not enabled by default 
> in XEN for all domUs with static allocation but instead requires the 
> 'direct-map' property to be present in the domU dt node, then such a 
> configuration is still valid.
> I thought that with this parameter it is much easier to setup (and 
> test) both configurations.
Thanks for the explanation. This makes sense to me. :)

In this case, can we remove the below snippet from your patch.

+        if test -z "${DOMU_DIRECT_MAP[$i]}"
+        then
+ DOMU_DIRECT_MAP[$i]=1
+        fi

The reason being if the user wants to set 'direct-map' prop in dts, then 
the user can specify it in the config.
Else, (by default) the direct-map will be set to false. This is inline 
with XEN's behavior as you described above.
- Ayan

- Ayan

> Xenia