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Re: NetBSD DomU (PV) hangs on Xen 4.13.1 / NetBSD 9.1



On Wed, 23 Dec 2020, Jarom√≠r Doleń~Mek wrote:
TL;DR ZFS + Xen doesn't work together under NetBSD 9.1. You need to
either use NetBSD-current, or use something other than ZFS.

Longer version: Xen under NetBSD up to 9.x had a limitation of 32KB
MAXBSIZE related to xbd(4), the Xen kernels had an option override to
force the lower limit. This limitation was removed in NetBSD-current.
ZFS is loaded as a module, and is compiled with default MAXBSIZE of
64kb, which doesn't work with the Xen kernel's 32KB.

But overriding as per http://mail-index.netbsd.org/port-xen/2020/09/11/msg009793.html works. What I don't get is why seeing as xen modules are distinct from non-xen (/stand/amd64/9.1/modules/zfs/zfs.kmod vs /stand/amd64-xen/9.1/modules/zfs/zfs.kmod), the xen versions cannot be built with this override automatically. The patch below would also impact non-Xen kernels.

I've not yet managed to follow through the build process to work out how amd64-xen kernel modules are built, I expect someone (hopefluly reading this list!) will know off the top of their head.


--- src/sys/modules/zfs/Makefile.zfsmod.DIST    2019-02-05 04:54:36.000000000 -0500
+++ src/sys/modules/zfs/Makefile.zfsmod 2020-09-10 18:35:34.683493656 -0400
@@ -135,5 +135,6 @@
 CPPFLAGS+=     -I${ZFSDIR}/dist/uts/common

 CPPFLAGS+=     -D_PROPLIB_ZFS_CONFLICT
+CPPFLAGS+=     -DMAXPHYS=32768

 NEED_ISYSTEM=  # duplicate headers, depends on -isystem to build


Le mer. 23 déc. 2020 à 11:04, Matthias Petermann <mp%petermann-it.de@localhost> a écrit :

Hello Brian,

Am 22.12.2020 um 18:51 schrieb Brian Buhrow:
      hello.  Just for giggles, what if you reduce the vcpu count to 1 to make sure you're not running into some sort of crazy race condition with the domu
or a constraint in the dom0?  If it works, then you can explore why a count of 8 doesn't.

I did that - but same effect here.

Anyway, during my tests I observed that one attempt with the ZVOL
renders the system in state in which even the file backed volume will
panic. After this, restarting xencommons doesn't help but a complete
system reboot will do.

Kind regards
Matthias



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