Re: [Xen-devel] REGRESSION: Xen 4.13 RC5 fails to bootstrap Dom0 on ARM

[Roman Shaposhnik <roman@xxxxxxxxxx>]

Hi Julien,

On Tue, Dec 17, 2019 at 3:30 AM Julien Grall <julien@xxxxxxx> wrote:
>
> Hi,
>
> On 17/12/2019 04:39, Roman Shaposhnik wrote:
> > On Mon, Dec 16, 2019 at 6:55 PM Stefano Stabellini
> > <sstabellini@xxxxxxxxxx> wrote:
> >> On Mon, 16 Dec 2019, Roman Shaposhnik wrote:
> >> If I sum all the memory sizes together I get 0x3ddfd000 which is 990M.
> >> If so, I wonder how you could boot succesfully with dom0_mem=1024M even
> >> on Xen 4.12... :-?
> >
> > That is a very interesting observation indeed! I actually don't
> > remember where that device tree came from, but I think it was from one
> > of the Linaro sites.
>
> This is mostly likely because of:
>
> commit 6341a674573f1834f083f0ab0f5b36b075f9e02e
> Author: Julien Grall <julien.grall@xxxxxxx>
> Date:   Wed Aug 21 22:42:31 2019 +0100
>
>      xen/arm: domain_build: Don't continue if unable to allocate all
> dom0 banks
>
>      Xen will only print a warning if there are memory unallocated when
> using
>      1:1 mapping (only used by dom0). This also includes the case where no
>      memory has been allocated.
>
>      It will bring to all sort of issues that can be hard to diagnostic for
>      users (the warning can be difficult to spot or disregard).
>
>      If the users request 1GB of memory, then most likely they want the
> exact
>      amount and not 512MB. So panic if all the memory has not been
> allocated.
>
>      After this change, the behavior is the same as for non-1:1 memory
>      allocation (used by domU).
>
>      At the same time, reflow the message to have the format on a single
>      line.
>
>      Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
>      Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

It seems you're absolutely right. Looking at the logs from Xen 4.12 I'm seeing:

(XEN) Allocating 1:1 mappings totalling 1024MB for dom0:
(XEN) WARNING: Failed to allocate requested dom0 memory. 624MB unallocated
(XEN) BANK[0] 0x00000008000000-0x00000010000000 (128MB)
(XEN) BANK[1] 0x00000036000000-0x0000003e000000 (128MB)
(XEN) BANK[2] 0x00000040000000-0x00000047000000 (112MB)
(XEN) BANK[3] 0x0000007b000000-0x0000007c000000 (16MB)
(XEN) BANK[4] 0x0000007e000000-0x0000007f000000 (16MB)
(XEN) Grant table range: 0x00000047998000-0x000000479d8000
(XEN) Allocating PPI 16 for event channel interrupt

So yes -- it was a warning that now turned an ERROR. So at least that
part is clear now.

What isn't clear still is the interplay between device trees and Xen
memory allocation -- I'll reply to Stefano on that.

Thanks,
Roman.

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