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Re: [Xen-devel] PV dom0 crash: kernel NULL pointer dereference in evtchn_from_irq

On 19.03.20 03:26, Marek Marczykowski-Górecki wrote:

 From time to time, during intensive tests I get the dom0 crash like
below. This is PV dom0, running on Xen nested inside KVM.
I don't really know when it started happening, I've got it on at least
those versions:
  - Xen 4.8.5 + Linux dom0 4.19.94
  - Xen 4.13.0 + Linux dom0 5.4.25
  - at least once also on physical hardware (Xen 4.13.0 + Linux dom0

Contrary to the other issue, here suspend is not involved, it is just
intensive system usage - multiple VM startups, involving some I/O,
network traffic etc. This happens rather rarely (I'd say about 1-3% of
To be honest, I'm not really sure if the bug is in Xen-related code at
all, or if Xen functions are in the call trace only because it is PV

Full crash message:

[14474.613706] BUG: kernel NULL pointer dereference, address: 000000000000001c
[14474.615832] #PF: supervisor read access in kernel mode
[14474.617321] #PF: error_code(0x0000) - not-present page
[14474.618702] PGD 0 P4D 0
[14474.619452] Oops: 0000 [#1] SMP NOPTI
[14474.620452] CPU: 0 PID: 431254 Comm: rm Not tainted 5.4.25-1.qubes.x86_64 #1
[14474.622900] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014
[14474.626322] RIP: e030:evtchn_from_irq+0x1f/0x40

I have seen this while testing some event channel related patches and
thought I was introducing this case. Seems as if it can happen even
without my patches.

I'll send the fixup I've added to my series soon.


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