Re: [arm] Dom0 hangs after enable KROBE_EVENTS and/or UPROBE_EVENTS in kernel config

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 23 Jul 2021, Julien Grall wrote:
> On 22/07/2021 22:39, Stefano Stabellini wrote:
> > On Thu, 22 Jul 2021, Julien Grall wrote:
> > > > You can go and edit 76085aff29f585139a37a10ea0a7daa63f70872c to change
> > > > from 4K to any multiple of 4K, e.g. 8K, 12K, 16K, 20K. They should all
> > > > work the same.
> > > > 
> > > > Looking at the boot logs on pastebin I noticed that Xen is not loaded at
> > > > a 2MB aligned address. I recommend you change Xen loading address to
> > > > 0x500200000. And the kernel loading address to 0x500400000.
> > > 
> > > I am curious to know why you recommend to load at 2MB aligned address. The
> > > Image protocol doesn't require to load a 2MB aligned address. In fact, we
> > > add
> > > issue on Juno because the bootloader would load Xen at a 4KB address. UEFI
> > > will also load at a 4KB align address.
> > 
> > It is from empirical evidence :-)
> 
> Right...
> 
> > I cannot tell you the exact reason but I saw "strange" problems in the
> > past that went away after choosing a 2MB alignment. So we settled for
> > using 2MB in ImageBuilder and we haven't seen any more issues.
> 
> It would have been good to report such issue back then so it could have been
> analyzed and possibly fixed.
> 
> > However, it could have been anything: a bug in U-Boot not relevant
> > anymore, a bug in Linux, etc. I don't know for sure.
> 
> This is the worrying part. We have a potential bug that no one knows why it
> happened. Can this be reproduced?

I managed to reproduce the problem. I switched ImageBuilder to use 4K
alignment (just by changing the variable "offset" at the top of
scripts/uboot-script-gen). It generated a boot.source file like this:

tftpb 0xC01000 2021.1/xen
tftpb 0xCEA000 2021.1/xen-Image-5.10
tftpb 0x18D1000 2021.1/initrd.cpio
tftpb 0x1A55000 2021.1/xen.dtb
[trimmed because the rest is not too relevant]


These are the sizes:

12479370 Jul  21 19:02 xen-Image-5.10
40577    Jul  21 18:25 xen.dtb
950280   Jul  19 16:58 xen
1586176  Jun  4  17:14 initrd.cpio


I did the calculations by hand and there are no overlaps. This is the
output from u-boot and boot log failure: https://pastebin.com/rbTBPn5g

Using 2MB works. I tried 1MB for curiosity and got a different
error: https://pastebin.com/UHFUHyxN

Do you think it is worth investigating further?

- Stefano