On Fri, 2012-08-17 at 08:58 +0200, Christian Schaubschl?ger wrote: > >> I bistcted that down to this patch: > >> > >> commit b566a22c23327f18ce941ffad0ca907e50a53d41 > >> Author: Khalid Aziz <khalid.aziz at hp.com> > >> Date: Fri Apr 27 13:00:33 2012 -0600 > >> > >> PCI: disable Bus Master on PCI device shutdown > >> > >> Disable Bus Master bit on the device in pci_device_shutdown() to ensure PCI > >> devices do not continue to DMA data after shutdown. This can cause memory > >> corruption in case of a kexec where the current kernel shuts down and > >> transfers control to a new kernel while a PCI device continues to DMA to > >> memory that does not belong to it any more in the new kernel. > >> > >> I have tested this code on two laptops, two workstations and a 16-socket > >> server. kexec worked correctly on all of them. > >> > >> Signed-off-by: Khalid Aziz <khalid.aziz at hp.com> > >> Signed-off-by: Bjorn Helgaas <bhelgaas at google.com> > >> > >> > >> Without this patch, int13 works fine here! If anyone needs more > >> information, just let me know! > > Which leads to an interesting conundrum. > > > > kexec appears to be more reliable for booting another kernel with this > > patch applied. This patch does kill the entier use case of making BIOS > > calls, and I suspect it also does nasty things to alpha bootloaders. > > > > My gut feel is that the trampoline code should reenable bus mastering > > on the devices that lie behind int13, but I don't know how practical > > that suggestion is in reality. > > One could make this patch optional... e.g. let kexec tell the running kernel whether or not to disable bus mastering before booting the new one (something like 'kexec --disable-bus-mastering -l /boot/new_kernel.bin'). Don't know if this would be practicable... > > Christian > Sorry, I have been on vacation and hadn't been watching mailing list. I would not want to make this patch optional. It will be difficult for most end users to tell if they should kexec with this enabled or not. I would rather fix issues caused by this patch. I will spend some time understanding the problem you are seeing and get back to you. Thanks -- Khalid Aziz <khalid.aziz at hp.com>
