On Tue, Feb 24, 2015 at 02:10:28PM +0000, Marc Zyngier wrote: > On 24/02/15 13:45, Richard W.M. Jones wrote: > > On Tue, Feb 24, 2015 at 01:12:49PM +0000, Marc Zyngier wrote: > >> Here's my theory: userspace is accessing something it should never > >> access (outside of RAM, basically), and doing so via a kernel interface. > >> > >> Is this process accessing /dev/mem by any chance? dmidecode anyone? > > > > Not as far as I know. The userspace process is inserting modules. > > > > Here is the userspace function which is most likely to be running: > > > > https://github.com/libguestfs/supermin/blob/master/src/init.c#L292 > > Hmmm. That seems quite inoffensive indeed... > > > Unfortunately because of lack of a full stack trace, I can't be sure > > exactly what system call is failing, but I'll probably add more debug > > to the userspace program later. > > > > BTW this worked fine in 3.19. It's started failing in 3.20/4.0. It > > also works fine on x86. > > Any chance you could find out whether that's a host or guest regression? Here is a summary of the test combinations that I have run: guest kernel host kernel result -------------------------------------------------------- 3.19.0-0.rc7 3.19.0-0.rc7 no bug seen 3.20.0-0.rc0 3.19.0-0.rc7 bug seen 3.19.0-0.rc7 4.0.0-0.rc1 no bug seen 4.0.0-0.rc1 4.0.0-0.rc1 bug seen So a guest regression, I think? It's also possible the bug existed in old kernels but was masked somehow, eg. different memory layout. I can probably bisect this given time, but I'm going to try putting some debug into the userspace process to find out which system call fails first. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
