Re: [Xen-devel] [XEN PATCH v1] libxl: Add DTB compatible list to config file

[Julien Grall <julien.grall@xxxxxxx>]

Hi Oleksandr,

On 16/10/2019 15:04, Oleksandr Grytsov wrote:
> On Fri, Oct 11, 2019 at 8:21 PM Stefano Stabellini
> <sstabellini@xxxxxxxxxx> wrote:
> > On Fri, 11 Oct 2019, Julien Grall wrote:
> > > Hi,
> > >
> > > On 11/10/2019 16:23, Ian Jackson wrote:
> > > > Oleksandr Grytsov writes ("[PATCH v1] libxl: Add DTB compatible list to
> > > > config file"):
> > > > > From: Oleksandr Grytsov <oleksandr_grytsov@xxxxxxxx>
> > > > >
> > > > > Some platforms need more compatible property values in device
> > > > > tree root node in addition to "xen,xenvm-%d.%d" and "xen,xenvm"
> > > > > values that are given by Xen by default.
> > > I am pretty sure I have seen this patch a few years ago, but I can't find it
> > > in my inbox. What is the exact problem here?
> > >
> > > > > Specify in domain configuration file which values should be added
> > > > > by providing "dtb_compatible" list of strings separated by comas.
> > > > Hi, thanks.
> > > >
> > > > I don't have an opinion about the principle of this and would like to
> > > > hear from ARM folks about that.
> > > >
> > > > Also, Stefano, Julien: should we be asking for a freeze exception for
> > > > this for 4.13 ?
> > > I don't have enough context to understand the exact issue he is trying to
> > > solve.
> > Same here. Is this patch needed because on some platform the OS checks
> > for the platform "model" (also known as "machine name") on device tree
> > before continuing or to trigger a difference behavior?
> Yes, exactly.
>
> I will redo the patch with Ian's comments if it is ok in general.
By specifying a different compatible (let say "renesas,r8a774a1"), then you 
claim that your virtual machine is exactly the same as that board.
This means, the OS is free to assume that the memory layout and all the devices 
are exactly the same. This is definitely not true as the virtual machine we 
expose is specific to Xen.
So I don't think this is the correct approach here. Can you provide a real-life 
example on why you need this?
Cheers,

--
Julien Grall

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