Re: [SeaBIOS] [PATCH] support piix PAM registers in KVM

[Jason Krieg]

On 06/15/2011 03:17 PM, Avi Kivity wrote:
> On 06/15/2011 02:58 PM, Jason Krieg wrote:
> > On 09/21/2010 02:31 PM, Gleb Natapov wrote:
> > > Without this BIOS fails to remap 0xf0000 memory from ROM to RAM so 
> > > writes
> > > to F-segment modify ROM content instead of memory copy. Since QEMU does
> > > not reloads ROMs during reset on next boot modified copy of BIOS is 
> > > used.
> > >
> > > Signed-off-by: Gleb Natapov
> > > diff --git a/hw/piix_pci.c b/hw/piix_pci.c
> > > index 933ad86..0bf435d 100644
> > > --- a/hw/piix_pci.c
> > > +++ b/hw/piix_pci.c
> > > @@ -99,10 +99,6 @@ static void 
> > > i440fx_update_memory_mappings(PCII440FXState *d)
> > >       int i, r;
> > >       uint32_t smram, addr;
> > > if (kvm_enabled()) {
> > >    /* FIXME: Support remappings and protection changes. */
> > >    return;
> > > }
> > >  update_pam(d, 0xf0000, 0x100000, (d->dev.config[I440FX_PAM]>>
> > >
> > > 4)&  3);
> > >       for(i = 0; i<  12; i++) {
> > >           r = (d->dev.config[(i>>  1) + (I440FX_PAM + 1)]>>  ((i&
> > > 4))&  3;
> >
> > Hi,
> >
> > While testing migration from old to new kvm ( 0.12.5 to 0.14.x ) and 
> > after fixing
> > some other problems mainly version_id probs in some of the 
> > VMStateDescriptions
> > everything was working fine until I tried to migrate Windows guests 
> > they would crash
> > after running some time. Linux guests are running stable.
> >
> > So I decided to do a git bisect to identify the according commit.
> > Reverting this commit fixes this problem with Windows guests.
> >
> > What consequences might it have not updating these memory mappings ?
>
> Resets may fail.
> > Does this commit need a specific seabios version, we have seabios 
> > 0.6.0 with qemu-kvm 0.12.5
> > and seabios 0.6.1.2 with qemu-kvm 0.14.1 ?
>
> IIUC newer seabios depends on this commit, but this commit does not 
> depend on seabios.
> > Maybe instead of reverting this commit one could check the seabios 
> > version in this method
> > and only do an update of these piix PAM registers if running with a 
> > newer seabios version ?
>
> It would be better to first understand what's going wrong.

I presume (just guessing) Windows wrote to F-segment modifying the ROM 
and now gets
confused if these PAM registers are updated.

Any ideas for what I could look for ?