Re: [Xen-devel] Xen 4.8.0 dom0pvh=1 causes ext4 filesystem corruption

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 03/09/2017 07:19 PM, Andrew Cooper wrote:
> On 10/03/2017 00:09, Steven Haigh wrote:
> > On 10/03/17 02:13, Valtteri Kiviniemi wrote:
> > > Hi,
> > >
> > > Yesterday I decided to upgrade my Xen version from 4.6.0 to 4.8.0. I
> > > compiled it from source and at the same time I compiled the latest Linux
> > > kernel (4.10.1).
> > >
> > > When rebooting I decided to try if dom0 PVH would work (with previous
> > > Xen version it just caused kernel panic). Seemed to boot fine until
> > > systemd started mounting the root filesystem and then the console was
> > > filled with ext4 errors. Couldn't even log in.
> > >
> > > Booting with a systemrescuecd and running fsck just caused the whole
> > > filesystem to be re-attached in thousands of small pieces under
> > > lost+found. I was sure that this was a some kind of hardware failure, so
> > > I switched my hard drives and did a clean reinstall for dom0 and tried
> > > again. Again, after a reboot the whole rootfs was completely corrupted.
> > >
> > > Second reinstall and this time I disabled dom0 PVH and the system booted
> > > just fine, and no ext4 errors. My root filesystem is just a simple Linux
> > > software raid1 with ext4 on top of it.
> > >
> > > Now that I started thinking I have also had strange ext4 errors
> > > happening inside my guests, so I also disabled PVH from all the guests.
> > > With guests the ext4 error is always the same: "EXT4-fs error (device
> > > xvda1): ext4_iget:4665: inode #317: comm find: bogus i_mode (135206)"
> > >
> > > Unfortunately I don't have any logs from the dom0 corruption as I can't
> > > even log in to the system when dom0 PVH is enabled. The corruption
> > > happens instantly during system bootup.
> > I have this happen a lot using pvh mode in previous Xen versions. Is it
> > supposed to be 'working' yet or is it still not recommended for use?
> That version of PVH has just been ripped out of Linux, and is in the
> process of being ripped out of the hypervisor.
>
> The replacement, accessed by using dom0=pvh is available in master, will
> be present in Xen 4.9, and should work with Linux 4.11 and FreeBSD
> Current.  (Roger, Boris - please correct me if I am wrong.)

There is nothing in Linux currently to support PVH dom0, only domU. I 
haven't tried booting dom0 in PVH mode yet but I doubt anything good 
will come out of this.
This is something I will be working on next.

-boris


> The same Linux and FreeBSD versions should function perfectly well as
> plain domUs in PVH mode, by selecting device_model=none in the domain
> configuration.  (Dom0 is rather more complicated than domU, due to the
> shared responsibility of real hardware with Xen.)
>
> ~Andrew
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