[SeaBIOS] A20: ahci_process_op is called with A20 off

[Paolo Bonzini]

On 10/05/2017 21:21, Kevin O'Connor wrote:
> On Tue, May 09, 2017 at 08:39:07PM +0000, Xu, Anthony wrote:
>> Hi All,
>>
>> I recently met an issue, I can't boot my centos guest in below scenarios.
>>
>> I disabled kvmvapic by
>>
>> diff --git a/hw/intc/apic_common.c b/hw/intc/apic_common.c
>> index c3829e3..52be2b0 100644
>> --- a/hw/intc/apic_common.c
>> +++ b/hw/intc/apic_common.c
>> @@ -440,7 +440,7 @@ static const VMStateDescription vmstate_apic_common = {
>>  static Property apic_properties_common[] = {
>>      DEFINE_PROP_UINT8("version", APICCommonState, version, 0x14),
>>      DEFINE_PROP_BIT("vapic", APICCommonState, vapic_control, VAPIC_ENABLE_BIT,
>> -                    true),
>> +                    false),
>>      DEFINE_PROP_BOOL("legacy-instance-id", APICCommonState, legacy_instance_id,
>>                       false),
>>      DEFINE_PROP_END_OF_LIST(),
>>
>>
>> I run Qemu in TCG mode
>>
>> ./x86_64-softmmu/qemu-system-x86_64 -bios /home/root/git/seabios/out/bios.bin -machine q35 
>>  -m 1G -drive format=raw,file=/home/root/images/centos7.2.img,if=ide,index=0 -nographic
>>  -nodefaults  -serial stdio -monitor pty
>>
>> It can't boot with below message,
>> "
>> Booting from Hard Disk...
>> WARNING - Timeout at ahci_command:154!
>> Boot failed: could not read the boot disk
>>
>> enter handle_18:
>>   NULL
>> Booting from Floppy...
>> Boot failed: could not read the boot disk
>> "
>>
>> Once I add kvmvapic , it can boot.
>>
>> I dig into seebios code, and found ahci_process_op is called with A20 off,
>>
>> The call trace is,
>> process_op_16->process_op_both->call32->call32_smm->process_op_32->ahci_process_op
>>
>> call32_smm calls call32_prep, but because the method is C16_SMM, A20 is not enabled in call32_prep.
>> ahci_process_op is called with A20 off.
> 
> As I understand it, entering System Managament Mode (SMM) should
> automatically enable A20, so it should not be necessary for call32_smm
> to enable it.  Are you sure the issue is related to A20 instead of
> some other issue with SMM?

This is a QEMU bug, it doesn't enable A20 in system management mode.

Paolo