boot hangs with 5.18.14-1~bpo11+1 and 5.18.16-1~bpo11+1

[spin <spin@massive.ch>]

Hello,

One of my stable+bpo machines boots fine with:

linux-image-5.18.0-0.bpo.1-amd64            5.18.2-1~bpo11+1

But hangs with:

linux-image-5.18.0-0.deb11.3-amd64          5.18.14-1~bpo11+1
linux-image-5.18.0-0.deb11.4-amd64          5.18.16-1~bpo11+1

I'm not sure about info to provide, but here is an excerpt of 
5.18.2-1~bpo11+1 booting:

kernel: [    1.171587] e1000e 0000:00:1f.6 0000:00:1f.6 (uninitialized): 
registered PHC clock
kernel: [    1.188702] i915 0000:00:02.0: enabling device (0006 -> 0007)
kernel: [    1.189347] i915 0000:00:02.0: [drm] VT-d active for gfx access
kernel: [    1.189349] checking generic (6000000000 21c0000) vs hw 
(6012000000 1000000)
kernel: [    1.189350] checking generic (6000000000 21c0000) vs hw 
(4000000000 10000000)

On hanging kernels, this would hang after the last i915 line, so no 
"checking generic" output.

Machine is an HP elitedesk 800 G8 with an 11th Gen Intel(R) Core(TM) 
i9-11900. The only things worth pointing out are that this machine has 
secureboot enabled and an nvidia gpu. Everything was fine up to 
5.18.2-1~bpo11+1.

On a first look, it appears relevant config changes between 
5.18.2-1~bpo11+1 and 5.18.14-1~bpo11+1 are mostly security/mitigations 
related. How should I proceed/diagnose/report further?

Any idea?

Thanks in advance

  spin