In my archlinux system, running as kvm guest on an archlinux host, I have problems with shared folders (using the "9p" file system), since I upgraded the kernel in my guest system to 3.11.1.

All shared folders are now in "read only" mode. Guests are no longer able to write.

I was able to fix this by switching "security_model", in the "-virtfs" parameter to qemu, from "passthrough" to "mapped", but then any try to execute a script from the mounted shared folder results in:

-bash: ./test.pl: /usr/bin/perl: bad interpreter: Numerical result out of range

I've downgraded the guest system to linux 3.10.9 and this immediately fixed this issue.

After doing so, I was able to switch back the security model to "passthrough". Writing works. Executing scripts from the mounted shared folder works, too.

For me it seems like "9p" is broken on Linux 3.11.1.

The host system is not affected. There, I can keep with 3.11.1 without causing any kvm problems.

Can someone please find out if there is a patch available for this and perhaps ship an updated kernel package?