* split lock issue in multiboot_dma.bin
@ 2025-08-07 12:15 Xiaoyao Li
2025-08-07 16:00 ` Xiaoyao Li
0 siblings, 1 reply; 3+ messages in thread
From: Xiaoyao Li @ 2025-08-07 12:15 UTC (permalink / raw)
To: Marcus Hähnel, Adam Lackorzynski, Paolo Bonzini
Cc: Xiaoyao Li, qemu-devel@nongnu.org, Philippe Mathieu-Daudé,
Chenyi Qiang
When running the kvm-unit-tests on Intel platforms with "split lock
disable" feature, every test triggers a kernel warning of
x86/split lock detection: #AC: qemu-system-x86_64/373232 took a
split_lock trap at address: 0x1e3
After investigation, it turns out the split lock happens from
multiboot_dma.bin:
Hack KVM by exiting to QEMU on split lock #AC, we get
KVM: exception 17 exit (error code 0x0)
EAX=00000001 EBX=00000000 ECX=00000014 EDX=0001fb80
ESI=00000000 EDI=000000a8 EBP=00000000 ESP=00006f10
EIP=000001e3 EFL=00010002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0900 00009000 0000ffff 00009300 DPL=0 DS16 [-WA]
CS =c000 000c0000 0000ffff 00009b00 DPL=0 CS16 [-RA]
SS =0000 00000000 0000ffff 00009300 DPL=0 DS16 [-WA]
DS =c000 000c0000 0000ffff 00009300 DPL=0 DS16 [-WA]
FS =0950 00009500 0000ffff 00009300 DPL=0 DS16 [-WA]
GS =06f2 00006f20 0000ffff 00009300 DPL=0 DS16 [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT= 000c02b4 00000027
IDT= 00000000 000003ff
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000
DR3=0000000000000000
DR6=00000000ffff0ff0 DR7=0000000000000400
EFER=0000000000000000
Code=89 16 08 00 65 66 0f 01 16 06 00 66 b8 01 00 00 00 0f 22 c0 <65> 66
ff 2e 00 00 b8 10 00 00 00 8e d0 8e d8 8e c0 8e e0 8e e8 66 b8 08 00 66
ba 10 05 66
And it matches with what disassembled from multiboo_dma.bin:
#objdump -b binary -m i386 -D pc-bios/multiboot_dma.bin
1d1: 08 00 or %al,(%eax)
1d3: 65 66 0f 01 16 lgdtw %gs:(%esi)
1d8: 06 push %es
1d9: 00 66 b8 add %ah,-0x48(%esi)
1dc: 01 00 add %eax,(%eax)
1de: 00 00 add %al,(%eax)
1e0: 0f 22 c0 mov %eax,%cr0
>1e3: 65 66 ff 2e ljmpw *%gs:(%esi)
1e7: 00 00 add %al,(%eax)
1e9: b8 10 00 00 00 mov $0x10,%eax
1ee: 8e d0 mov %eax,%ss
1f0: 8e d8 mov %eax,%ds
1f2: 8e c0 mov %eax,%es
1f4: 8e e0 mov %eax,%fs
1f6: 8e e8 mov %eax,%gs
1f8: 66 b8 08 00 mov $0x8,%ax
1fc: 66 ba 10 05 mov $0x510,%dx
I don't know where the multiboot_dma.bin are built from so that I cannot
further help resolve the split lock issue.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: split lock issue in multiboot_dma.bin
2025-08-07 12:15 split lock issue in multiboot_dma.bin Xiaoyao Li
@ 2025-08-07 16:00 ` Xiaoyao Li
2025-08-08 4:04 ` Xiaoyao Li
0 siblings, 1 reply; 3+ messages in thread
From: Xiaoyao Li @ 2025-08-07 16:00 UTC (permalink / raw)
To: Marcus Hähnel, Adam Lackorzynski, Paolo Bonzini
Cc: qemu-devel@nongnu.org, Philippe Mathieu-Daudé, Chenyi Qiang
On 8/7/2025 8:15 PM, Xiaoyao Li wrote:
> When running the kvm-unit-tests on Intel platforms with "split lock
> disable" feature, every test triggers a kernel warning of
>
> x86/split lock detection: #AC: qemu-system-x86_64/373232 took a
> split_lock trap at address: 0x1e3
>
> After investigation, it turns out the split lock happens from
> multiboot_dma.bin:
>
> Hack KVM by exiting to QEMU on split lock #AC, we get
>
> KVM: exception 17 exit (error code 0x0)
> EAX=00000001 EBX=00000000 ECX=00000014 EDX=0001fb80
> ESI=00000000 EDI=000000a8 EBP=00000000 ESP=00006f10
> EIP=000001e3 EFL=00010002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
> ES =0900 00009000 0000ffff 00009300 DPL=0 DS16 [-WA]
> CS =c000 000c0000 0000ffff 00009b00 DPL=0 CS16 [-RA]
> SS =0000 00000000 0000ffff 00009300 DPL=0 DS16 [-WA]
> DS =c000 000c0000 0000ffff 00009300 DPL=0 DS16 [-WA]
> FS =0950 00009500 0000ffff 00009300 DPL=0 DS16 [-WA]
> GS =06f2 00006f20 0000ffff 00009300 DPL=0 DS16 [-WA]
> LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
> TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
> GDT= 000c02b4 00000027
> IDT= 00000000 000003ff
> CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
> DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000
> DR3=0000000000000000
> DR6=00000000ffff0ff0 DR7=0000000000000400
> EFER=0000000000000000
> Code=89 16 08 00 65 66 0f 01 16 06 00 66 b8 01 00 00 00 0f 22 c0 <65> 66
> ff 2e 00 00 b8 10 00 00 00 8e d0 8e d8 8e c0 8e e0 8e e8 66 b8 08 00 66
> ba 10 05 66
>
> And it matches with what disassembled from multiboo_dma.bin:
>
> #objdump -b binary -m i386 -D pc-bios/multiboot_dma.bin
>
> 1d1: 08 00 or %al,(%eax)
> 1d3: 65 66 0f 01 16 lgdtw %gs:(%esi)
> 1d8: 06 push %es
> 1d9: 00 66 b8 add %ah,-0x48(%esi)
> 1dc: 01 00 add %eax,(%eax)
> 1de: 00 00 add %al,(%eax)
> 1e0: 0f 22 c0 mov %eax,%cr0
> >1e3: 65 66 ff 2e ljmpw *%gs:(%esi)
> 1e7: 00 00 add %al,(%eax)
> 1e9: b8 10 00 00 00 mov $0x10,%eax
> 1ee: 8e d0 mov %eax,%ss
> 1f0: 8e d8 mov %eax,%ds
> 1f2: 8e c0 mov %eax,%es
> 1f4: 8e e0 mov %eax,%fs
> 1f6: 8e e8 mov %eax,%gs
> 1f8: 66 b8 08 00 mov $0x8,%ax
> 1fc: 66 ba 10 05 mov $0x510,%dx
>
> I don't know where the multiboot_dma.bin are built from so that I cannot
> further help resolve the split lock issue.
stupid me. The src code is just pc-bios/optionrom/multiboot.S
But I don't know how to build a bin file from it to test my fix.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: split lock issue in multiboot_dma.bin
2025-08-07 16:00 ` Xiaoyao Li
@ 2025-08-08 4:04 ` Xiaoyao Li
0 siblings, 0 replies; 3+ messages in thread
From: Xiaoyao Li @ 2025-08-08 4:04 UTC (permalink / raw)
To: Marcus Hähnel, Adam Lackorzynski, Paolo Bonzini
Cc: qemu-devel@nongnu.org, Philippe Mathieu-Daudé, Chenyi Qiang
On 8/8/2025 12:00 AM, Xiaoyao Li wrote:
> On 8/7/2025 8:15 PM, Xiaoyao Li wrote:
>> When running the kvm-unit-tests on Intel platforms with "split lock
>> disable" feature, every test triggers a kernel warning of
>>
>> x86/split lock detection: #AC: qemu-system-x86_64/373232 took a
>> split_lock trap at address: 0x1e3
>>
>> After investigation, it turns out the split lock happens from
>> multiboot_dma.bin:
>>
>> Hack KVM by exiting to QEMU on split lock #AC, we get
>>
>> KVM: exception 17 exit (error code 0x0)
>> EAX=00000001 EBX=00000000 ECX=00000014 EDX=0001fb80
>> ESI=00000000 EDI=000000a8 EBP=00000000 ESP=00006f10
>> EIP=000001e3 EFL=00010002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
>> ES =0900 00009000 0000ffff 00009300 DPL=0 DS16 [-WA]
>> CS =c000 000c0000 0000ffff 00009b00 DPL=0 CS16 [-RA]
>> SS =0000 00000000 0000ffff 00009300 DPL=0 DS16 [-WA]
>> DS =c000 000c0000 0000ffff 00009300 DPL=0 DS16 [-WA]
>> FS =0950 00009500 0000ffff 00009300 DPL=0 DS16 [-WA]
>> GS =06f2 00006f20 0000ffff 00009300 DPL=0 DS16 [-WA]
>> LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
>> TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
>> GDT= 000c02b4 00000027
>> IDT= 00000000 000003ff
>> CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
>> DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000
>> DR3=0000000000000000
>> DR6=00000000ffff0ff0 DR7=0000000000000400
>> EFER=0000000000000000
>> Code=89 16 08 00 65 66 0f 01 16 06 00 66 b8 01 00 00 00 0f 22 c0 <65>
>> 66 ff 2e 00 00 b8 10 00 00 00 8e d0 8e d8 8e c0 8e e0 8e e8 66 b8 08
>> 00 66 ba 10 05 66
>>
>> And it matches with what disassembled from multiboo_dma.bin:
>>
>> #objdump -b binary -m i386 -D pc-bios/multiboot_dma.bin
>>
>> 1d1: 08 00 or %al,(%eax)
>> 1d3: 65 66 0f 01 16 lgdtw %gs:(%esi)
>> 1d8: 06 push %es
>> 1d9: 00 66 b8 add %ah,-0x48(%esi)
>> 1dc: 01 00 add %eax,(%eax)
>> 1de: 00 00 add %al,(%eax)
>> 1e0: 0f 22 c0 mov %eax,%cr0
>> >1e3: 65 66 ff 2e ljmpw *%gs:(%esi)
>> 1e7: 00 00 add %al,(%eax)
>> 1e9: b8 10 00 00 00 mov $0x10,%eax
>> 1ee: 8e d0 mov %eax,%ss
>> 1f0: 8e d8 mov %eax,%ds
>> 1f2: 8e c0 mov %eax,%es
>> 1f4: 8e e0 mov %eax,%fs
>> 1f6: 8e e8 mov %eax,%gs
>> 1f8: 66 b8 08 00 mov $0x8,%ax
>> 1fc: 66 ba 10 05 mov $0x510,%dx
>>
>> I don't know where the multiboot_dma.bin are built from so that I
>> cannot further help resolve the split lock issue.
>
> stupid me. The src code is just pc-bios/optionrom/multiboot.S
> But I don't know how to build a bin file from it to test my fix.
I resolve it myself. It turns out my machine lacks some crosscc package.
QEMU can build optionroms after I install g++-multilib．
I then verified my fix and sent it:
https://lore.kernel.org/qemu-devel/20250808035027.2194673-1-xiaoyao.li@intel.com/
^ permalink raw reply [flat|nested] 3+ messages in thread
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