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[SeaBIOS] A20: ahci_process_op is called with A20 off

Xu, Anthony posted 1 patch 8 years ago
Failed in applying to current master (apply log)
[SeaBIOS] A20: ahci_process_op is called with A20 off
Posted by Xu, Anthony 8 years ago 
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.

ahci_process_op accesses memory mapped IO to operate ahci, the IO is mapped to 0xfebff000, 
because a20 is disabled,  the bit 20 of 0xfebff000 is set 0 , which is 0xfeaff000, 
an iotlb entry mapping 0xfebff000 to 0xfeaff000 is added to iotlb cache. So ahci_process_op actually
accesses 0xfeaff000, it obviously won't work.

target/i386/helper.c

do_mapping:
    pte = pte & env->a20_mask;

Why does guest boot with kvmvapic?
In above scenario, there is no option roms.
After adding kvmvapic, there is one option rom kvmvapic rom, and __callrom is called for kvmvapic rom.
__callrom->farcall16big-> call16_override,

once call16_override is called, a20 is enabled and will not be disabled.
So ahci_process_op is called with a20 on.

I tried below change,  guest can boot without kvmvapic. I'm not familiar with seabios code, 
I don't consider it as a patch, but it proves my analysis is correct. With the change, __call32 calls
call32_prep with method  C16_BIG to enable a20 before calling ahci_process_op.

please help fix this issue.

Thanks,
Anthony

diff --git a/src/stacks.c b/src/stacks.c
index ef6a707..0949652 100644
--- a/src/stacks.c
+++ b/src/stacks.c
@@ -232,10 +237,11 @@ u32 VISIBLE16
 __call32(void *func, u32 eax, u32 errret)
 {
     ASSERT16();
-    if (CONFIG_CALL32_SMM && GET_GLOBAL(HaveSmmCall32))
-        return call32_smm(func, eax);
+//    if (CONFIG_CALL32_SMM && GET_GLOBAL(HaveSmmCall32))
+//        return call32_smm(func, eax);
     // Jump direclty to 32bit mode - this clobbers the 16bit segment
     // selector registers.













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Re: [SeaBIOS] A20: ahci_process_op is called with A20 off
Posted by Kevin O'Connor 7 years, 12 months ago 
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?

-Kevin

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Re: [SeaBIOS] A20: ahci_process_op is called with A20 off
Posted by Paolo Bonzini 7 years, 12 months ago 

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

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