Re: [PATCH] support piix PAM registers in KVM

Jason Krieg
2011-06-15T13:54:21Z

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<gleb@redhat.com>
>>> 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&
>>> 1) * 4))& 3;
>>> --
>>> Gleb.
>>> --
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>>
>> 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 ?