Re: [Qemu-arm] [RFC PATCH 0/4] ARM virt: ACPI memory hotplug support

[Auger Eric]

Hi Laszlo,

On 2/27/19 9:14 PM, Laszlo Ersek wrote:
> On 02/27/19 13:55, Shameerali Kolothum Thodi wrote:
>> Hi Laszlo,
>>
>>> -----Original Message-----
>>> From: Shameerali Kolothum Thodi
>>> Sent: 25 February 2019 09:54
>>> To: 'Laszlo Ersek' <address@hidden>; Auger Eric <address@hidden>;
>>> address@hidden; address@hidden;
>>> address@hidden; address@hidden; address@hidden
>>> Cc: xuwei (O) <address@hidden>; Linuxarm <address@hidden>; Ard
>>> Biesheuvel <address@hidden>; Leif Lindholm (Linaro address)
>>> <address@hidden>
>>> Subject: RE: [RFC PATCH 0/4] ARM virt: ACPI memory hotplug support
>>
>> [...]
>>  
>>>>>> The root cause seems to be EDK2 ACPI table checksum failure
>>>>>> as NFIT table is getting updated on hot-add. This needs further
>>>>>> investigation.
>>>>> + Ard, Leif, Laszlo if they have any idea of what is missing/wrong.
>>>>
>>>> Huh, very interesting; I usually don't expect my sanity checks to fire
>>>> in practice. :)
>>>>
>>>> The message
>>>>
>>>>   ProcessCmdAddChecksum: invalid checksum range in "etc/acpi/tables"
>>>>
>>>> is logged by OVMF's and ArmVirtQemu's ACPI Platform DXE Driver when it
>>>> finds an invalid COMMAND_ADD_CHECKSUM command in QEMU's ACPI
>>>> linker/loader script.
>>>>
>>>> Please see the command definition in QEMU's
>>>> "hw/acpi/bios-linker-loader.c". In particular, please refer to the
>>>> function bios_linker_loader_add_checksum(), which builds the command
>>>> structure, and documents the fields.
>>>>
>>>> (You may also refer to QEMU_LOADER_ADD_CHECKSUM in file
>>>> "OvmfPkg/AcpiPlatformDxe/QemuLoader.h" in the edk2 source tree, for the
>>>> same information.)
>>>>
>>>> The error message is logged if:
>>>> - the offset at which the checksum should be stored falls outside of the
>>>> size of the fw_cfg blob, or
>>>> - the range over which the checksum should be calculated falls outside
>>>> (at least in part) of the fw_cfg blob.
>>>>
>>>> To me this suggests that QEMU generates an invalid
>>>> COMMAND_ADD_CHECKSUM
>>>> command for the firmware.
>>>>
>>>> ... I've tried to skim the patches briefly. I think there must be an
>>>> error in the DSDT building logic that is only active on reboot if an
>>>> nvdimm module was hot-added before the reboot.
>>>
>>> Thanks for taking a look and the pointers. I will debug this further
>>> and get back.
>>
>> The root cause of the issue seems to be UEFI not seeing the updated acpi
>> table blob size on reboot once a new NFIT table is added(nvdimm hot added).
>>
>> Please see the debug logs below,
>>
>> Initial Guest boot
>> ---------------------------
>>
>> Debug logs from Qemu:
>>
>> build_header: acpi sig DSDT len 0x5127
>> build_header: acpi sig FACP len 0x10c
>> build_header: acpi sig APIC len 0xa8
>> build_header: acpi sig GTDT len 0x60
>> build_header: acpi sig MCFG len 0x3c
>> build_header: acpi sig SPCR len 0x50
>> build_header: acpi sig SRAT len 0x92
>> build_header: acpi sig SSDT len 0x38f
>> build_header: acpi sig XSDT len 0x5c
>> virt_acpi_build: acpi table_blob len 0x5844
>>
>> Debug logs from UEFI:
>>
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x9 Start=0x0 
>> Length=0x5127 Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x5130 
>> Start=0x5127 Length=0x10C Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x523C 
>> Start=0x5233 Length=0xA8 Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x52E4 
>> Start=0x52DB Length=0x60 Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x5344 
>> Start=0x533B Length=0x3C Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x5380 
>> Start=0x5377 Length=0x50 Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x53D0 
>> Start=0x53C7 Length=0x92 Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x5462 
>> Start=0x5459 Length=0x38F Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x57F1 
>> Start=0x57E8 Length=0x5C Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/rsdp" ResultOffset=0x8 Start=0x0 
>> Length=0x14 Blob->Size=0x24
>> ProcessCmdAddChecksum: File="etc/acpi/rsdp" ResultOffset=0x20 Start=0x0 
>> Length=0x24 Blob->Size=0x24
>> InstallQemuFwCfgTables: installed 8 tables
>>
>> Guest Reboot after ndimm hot added
>> ------------------------------------
>>
>> Debug logs from Qemu:
>>
>> build_header: acpi sig DSDT len 0x5127
>> build_header: acpi sig FACP len 0x10c
>> build_header: acpi sig APIC len 0xa8
>> build_header: acpi sig GTDT len 0x60
>> build_header: acpi sig MCFG len 0x3c
>> build_header: acpi sig SPCR len 0x50
>> build_header: acpi sig SRAT len 0x92
>> build_header: acpi sig SSDT len 0x38f
>> build_header: acpi sig NFIT len 0xe0  -->New
>> build_header: acpi sig XSDT len 0x64
>> virt_acpi_build: acpi table_blob len 0x592c -->blob len updated
>>
>> Debug logs from UEFI:
>>
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x9 Start=0x0 
>> Length=0x5127 Blob->Size=0x5844  -->Wrong blob size.
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x5130 
>> Start=0x5127 Length=0x10C Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x523C 
>> Start=0x5233 Length=0xA8 Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x52E4 
>> Start=0x52DB Length=0x60 Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x5344 
>> Start=0x533B Length=0x3C Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x5380 
>> Start=0x5377 Length=0x50 Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x53D0 
>> Start=0x53C7 Length=0x92 Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x5462 
>> Start=0x5459 Length=0x38F Blob->Size=0x5844
>> ProcessCmdAddChecksum: File="etc/acpi/tables" ResultOffset=0x57F1 
>> Start=0x57E8 Length=0xE0 Blob->Size=0x5844
>> ProcessCmdAddChecksum: invalid checksum range in "etc/acpi/tables"
>> OnRootBridgesConnected: InstallAcpiTables: Protocol Error
>>
>>
>> To me it seems on ARM vit acpi path, the blob len is calculated based
>> on actual tables and is updated only in virt_acpi_setup() --> 
>> acpi_add_rom_blob()
>> path. I had a look at the x86 code and it looks like, there, the blob len 
>> gets updated
>> with an additional buffer to take care of table resizing[1].
>>
>> As a hack i added the same to ARM virt and it seems to resolve the issue.
>> I am not sure this is the best approach to fix this though.
>>
>> Please let me know your thoughts.
>>
>> Thanks,
>> Shameer
>>
>> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
>> index 132414c..4291553 100644
>> --- a/hw/arm/virt-acpi-build.c
>> +++ b/hw/arm/virt-acpi-build.c
>> @@ -50,6 +50,8 @@
>>  #define ARM_SPI_BASE 32
>>  #define ACPI_POWER_BUTTON_DEVICE "PWRB"
>>
>> +#define ACPI_BUILD_TABLE_SIZE    0x20000
>> +
>>  static void acpi_dsdt_add_cpus(Aml *scope, int smp_cpus)
>>  {
>>      uint16_t i;
>> @@ -886,6 +888,10 @@ void virt_acpi_build(VirtMachineState *vms, 
>> AcpiBuildTables *tables)
>>          build_rsdp(tables->rsdp, tables->linker, &rsdp_data);
>>      }
>>
>> +    /* Make sure we have a buffer in case we need to resize the tables. */
>> +    g_array_set_size(tables_blob, ROUND_UP(acpi_data_len(tables_blob),
>> +                     ACPI_BUILD_TABLE_SIZE));
>> +
>>      /* Cleanup memory that's no longer used. */
>>      g_array_free(table_offsets, true);
>>  }
>>
>> [1] https://github.com/qemu/qemu/blob/master/hw/i386/acpi-build.c#L2792
> 
> Nice analysis, thanks.
> 
> I think the line that you reference, i.e.
> 
>   acpi_align_size(tables_blob, ACPI_BUILD_TABLE_SIZE);
> 
> in acpi_build() [hw/i386/acpi-build.c] masks this issue for x86 only as
> a side effect. To my understanding, the alignment / padding exists there
> for migration compatibility. It doesn't exist for updating the size of
> the ACPI blobs in fw_cfg across reboots. The issue is masked because the
> alignment is large enough (un-changed) to contain the regenerated blobs
> as well.>
> Given that the "virt" machine type is versioned, I think migration
> compat is a valid concern there too. This in itself would justify a
> similar padding.
I don't understand the migration compat issue. Please could you elaborate?
> 
> I don't know if we want to specifically care about size-changing
> ACPI-regen across reboot. I believe measures for that specific use case
> don't exist in x86 machine types either.
The NFIT redimensioning should exit on x86 too?
> 
> Another trick that is occasionally used (but might not apply here, I'm
> uncertain) is to always generate the relevant ACPI objects, but, in case
> they are not justified for the virtual hardware config, invalidate them
> by overwriting particular parts of them (for example, one or two bytes
> of their names). Hopefully this shouldn't introduce ACPI or AML errors,
> just make the ACPI interpreter ignore the affected objects.

Thanks!

Eric
> 
> Thanks,
> Laszlo
>