On Fri, Oct 09, 2009 at 01:49:03PM +0200, Gleb Natapov wrote: > On Fri, Oct 09, 2009 at 12:13:00PM +0200, Michael S. Tsirkin wrote: > > On Fri, Oct 09, 2009 at 09:00:49AM +0200, Gleb Natapov wrote: > > > On Fri, Oct 09, 2009 at 08:43:59AM +0200, Michael S. Tsirkin wrote: > > > > On Thu, Oct 08, 2009 at 07:40:12PM +0100, Jamie Lokier wrote: > > > > > Avi Kivity wrote: > > > > > > On 10/08/2009 06:06 PM, Michael S. Tsirkin wrote: > > > > > > >On Thu, Oct 08, 2009 at 05:29:29PM +0200, Avi Kivity wrote: > > > > > > > > > > > > > >>On 10/08/2009 04:52 PM, Michael S. Tsirkin wrote: > > > > > > >> > > > > > > >>>PCI memory should be disabled at reset, otherwise > > > > > > >>>we might claim transactions at address 0. > > > > > > >>>I/O should also be disabled, although for cirrus > > > > > > >>>it is harmless to enable it as we do not > > > > > > >>>have I/O bar. > > > > > > >>> > > > > > > >>>Note: need bios fix for this patch to work: > > > > > > >>>currently pc-bios incorrently assumes that it does not > > > > > > >>>need to enable i/o unless device has i/o bar. > > > > > > >>> > > > > > > >>>Signed-off-by: Michael S. Tsirkin<mst@xxxxxxxxxx> > > > > > > >> > > > > > > >>This needs to be conditional on the machine type. Old machines must > > > > > > >>retain this code for live migration to work (we need to live migrate the > > > > > > >>bios, so we can't assume the bios fix is in during live migration from > > > > > > >>older qemus). > > > > > > >> > > > > > > >No, if you migrate from older qemu you will be fine as command > > > > > > >is enabled there on init. > > > > > > > > > > > > > > > > > > > Right. > > > > > > > > > > No, I think Avi was right the first time. > > > > > > > > > > Migrating from an older qemu will be fine at first, but at the next > > > > > reset _following_ migration, it'll be running the old BIOS on a new > > > > > qemu and fail. > > > > > > > > > > -- Jamie > > > > > > > > I think this just means that there's another bug. > > > > On reset BIOS should be re-read from flash. > > > > qemu instead keeps it in RAM, this means that if > > > > guest corrupts it, or BIOS itself runs self-modifying > > > > code (which is not uncommon btw), bad things happen. > > > > > > > How do you know it is not uncommon (or happens at all?) > > > > I know memory corruptions are not uncommon, from experience :) > > > I don't see how from presence of memory corruptions you made a > conclusion that BIOSes run self-modifying code. > > > If BIOS is not shadowed it runs directly from ROM. Hard to use > > > self-modifying code there. > > > > Sorry I don't really know how this is handled in qemu. > > Can it run BIOS from ROM? Is ROM content sent over for migration? > Yes it can. There is no much difference between ROM and RAM in qemu > though. I don't know if ROM content is sent over for migration, but > IMHO it shouldn't. This will solve the problem we currently discuss. > Shadowed BIOS should be copied of course. Interesting. OTOH this means that after migration, shadowed BIOS and ROM are different. In theory, this can create problems. In practice I doubt this. > > I see this > > ret = load_image(filename, qemu_get_ram_ptr(bios_offset)); > > which seems to always load BIOS into RAM. > > Maybe I misunderstand. Could you enlighten me please? > Enlighten you about what? BIOS copies itself into shadow ram. At least > BOCHS bios does. I hope seabios does the same. People were implying changing BIOS triggers migration/reset issues. Do you think so too? > > > > > > We should fix qemu to re-read bios from flash. > > > > Makes sense? > > > > > > > We have option_rom_setup_reset() already. > > > > We don't, anymore :) > We are fast! Well, we surely have something similar instead. > > > > > > Don't we use it for BIOSes > > > too? > > > > > > > More long-term, we have duplication between reset and init > > > > routines. Maybe devices really should have init and cleanup, > > > > and on reset we'd cleanup all devices and then init them again? > > > > There are cases where state needs to be persistent across > > > > resets (VPD comes to mind) but these are rare, > > > > and probably need to be backed by writing to file anyway? > > > > > > > > > > > > -- > > > > MST > > > > > > > > -- > > > > To unsubscribe from this list: send the line "unsubscribe kvm" in > > > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > > > -- > > > Gleb. > > -- > Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
