* Philipp Hahn (h...@univention.de) wrote: > Hello, > > Am 15.08.2017 um 13:25 schrieb Laszlo Ersek: > > On 08/14/17 20:39, Dr. David Alan Gilbert wrote: > >> * Philipp Hahn (h...@univention.de) wrote: > >>> I'm currently investigating a problem, were a Linux VM does not reboot > >>> and gets stuck in the SeaBIOS reboot code: > >>> > >>> I'm using SeaBIOS-1.7 from Debian with a more modern qemu-2.8 > ...>>> If I dump both regions and compare them, I get a difference: > ...>> You might want seabios commit c68aff5 and b837e6 that got fixed after > >> I tracked down some reboot hangs - although they were rare, not every > >> time. c68aff5 did certainly cause a corruption, and the address of that > >> corruption was determined at link time and could overlay random useful > >> bits of code if you were unlucky. > > Thanks you for the commit IDs - to me this looks like they fixed the > problem. Testing with seabios-1.10 does not show any reboot problem so far. > > >>> 1. How can it be, that the low-mem ROM mapping is modified? > >> > >> I can't remember all the details, but PC ROM is shadowed and mapped over > >> with RAM at various times, > > > > Right. I don't remember for sure, but I believe the state of the PAM > > registers doesn't only affect what the VCPUs see in that address range, > > but also what your monitor commands will dump. (This would be the > > logical choice -- make the monitor output what the VCPUs see anyway, at > > the moment, dependent on the PAM settings.) > > That makes sense. > Do you know by change what change in Qemu triggered that bug, as I've > never seen any reboot problem with qemu-1.1.2, but only since switching > to qemu-2.8?
I didn't go back as far as 1.1.2, but I tried bisecting around 2.4/2.6 before I understood the failure and the bisect was very flaky; I think in the end it's a timing race where it comes down to the exact corrupt value; going back to ancient qemu might be taking some other path through seabios but I ddin't investigate. Dave > Thanks again for your excellent help. > > Philipp -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK