On 28/08/2025 11:22 am, Jan Beulich wrote:
> On 28.08.2025 12:01, Andrew Cooper wrote:
>> On 28/08/2025 8:07 am, Jan Beulich wrote:
>>> On 27.08.2025 19:47, Andrew Cooper wrote:
>>>> On 22/08/2025 2:47 pm, Teddy Astie wrote:
>>>>> Currently, hvmloader uses SMBIOS 2.4, however, when using OVMF, the
>>>>> SMBIOS is patched to 2.8, which has clarified the UUID format (as GUID).
>>>>>
>>>>> In Linux, if the SMBIOS version is >= 2.6, the GUID format is used, else
>>>>> (undefined as per SMBIOS spec), big endian is used (used by Xen).
>>>>> Therefore,
>>>>> you have a endian mismatch causing the UUIDs to mismatch in the guest.
>>>>>
>>>>> $ cat /sys/hypervisor/uuid
>>>>> e865e63f-3d30-4f0b-83e0-8fdfc1e30eb7
>>>>> $ cat /sys/devices/virtual/dmi/id/product_uuid
>>>>> 3fe665e8-303d-0b4f-83e0-8fdfc1e30eb7
>>>>> $ cat /sys/devices/virtual/dmi/id/product_serial
>>>>> e865e63f-3d30-4f0b-83e0-8fdfc1e30eb7
>>>>>
>>>>> This patch updates the SMBIOS version from 2.4 to 2.6 and fixup the UUID
>>>>> written in the table; which effectively fix this endianness mismatch with
>>>>> OVMF; while the UUID displayed by Linux is still the same for SeaBIOS.
>>>>>
>>>>> Signed-off-by: Teddy Astie <teddy.as...@vates.tech>
>>>>> ---
>>>>> This effectively changes the UUID seen with UEFI guests as it was
>>>>> actually inconsistent with SeaBIOS and SMBIOS expectations.
>>>>> ---
>>>> I agree this is a real bug and needs fixing.
>>> Hmm, I didn't realize this is a bug, and hence put the patch off as 4.22
>>> material. If there is a bug being fixed: Teddy, please add a Fixes: tag.
>> I'm not sure if this has a reasonable Fixes tag.
>>
>> It's a combination of an ill-specified domain handle format, and using
>> an ill-specified version of the SMBios spec.
> But the problem was still introduced into the code base at some point. Afaict
> in c683914ef913 ("Add code to generate SMBIOS tables to hvmloader"), i.e. when
> smbios.c was first added.
The thing that changed was the SMBios spec, in version 2.6. It went
from having an ill-defined statement of what a UUID was (and for which
Xen's code was a valid interpretation), to stating a MSFT GUID format.
~Andrew
