Re: Dom0 - fatal page fault in supervisor mode when root FS is on a slice of disklabel lying on a raidframe device, built up from two GPT wedges

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Thu, Aug 23, 2018 at 12:29:59PM +0200, Matthias Petermann wrote:
> Hello everybody,
> 
> After I described to netbsd-users yesterday[1] my problem with a certain
> configuration of NetBSD with Xen, the thought came to me that the port-xen
> list may be the more suitable place for it.
> 
> In the meantime, I have been able to narrow down the problem a bit more
> precisely. My original post is that Xen with NetBSD as Dom0 brings a kernel
> panic (page fault) to one and the same system when the root filesystem is
> inside a disklabel lying on a raidframe mirror, which in turn is made up of
> two components is present as GPT partitions. A comparable setup without the
> raidframe mirror doesn't have this issue.
> 
> Various assumptions have not been confirmed, in further attempts I could
> narrow the problem as follows:
> 
> 1) Works perfectly:
> * NetBSD / Xen 8.0-RELEASE Dom0
> * Xen 4.11
> * a single disk, GPT partitioned
> * Root file system within the first GPT partition (dk0)
> * BIOSboot (gpt biosboot .....) because the system has no UEFI BIOS, but the
> hard disk requires GPT due to its size (3 TB)
> 
> 2) Bring the kernel panic:
> * NetBSD / Xen 8.0-RELEASE Dom0
> * Xen 4.11
> * two disks, GPT partitioned
> * raidframe mirror raid0 consisting of the first GPT partition of each hard
> disk
> * A disklabel within the raid0
> * Root file system within the slice raid0a
> * BIOSboot (gpt biosboot .....) because the system has no UEFI BIOS, but the
> hard disk requires GPT due to its size (3 TB)
> 
> Interesting:
> If variant 2) without Xen but with the standard kernel of NetBSD 8.0 / amd64
> booted, there is no problem.
> 
> Does anyone have any idea what could be the cause here? I would like to
> understand how Dom0 accesses the root filesystem or the underlying devices.

did you pass the appropriate root= argument to the NetBSD kernel in the
Xen case ? The dom0 can't easily guess the right boot device in this
case, and it's possible it's using the wrong one.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--