smbios entry point auto on pc-i440fx

smbios entry point auto on pc-i440fx

[Pierre-Samuel LE STANG]

Hello team, 

I'm facing the issue of windows instances not beeing able of retrieving
the uuid because of smbios 3.0 (qemu 8.2 on debian openstack/libvirt).
The instances are of pc-i440fx-8.2 machine type.

If I understand well since 8.1 qemu use a 64bit format for the smbios
v3 which is not handle by windows OS.

I also found some commit about handling automatically the format by qemu
on q35 machine type to resolve this bug startting to 9.0.0 version
https://gitlab.com/qemu-project/qemu/-/issues/2008 

It seems forced to 64 bit on pc-i440fx-8.1 and above while forced to 32
under.

Is there a reason to not handle it automatically on pc-i440fx machine
type?

Is it safe to keep it to 32 for machine type pc-i440fx-8.1 and above?

Cheers!

-- 
PS Le Stang

Re: smbios entry point auto on pc-i440fx

[Daniel P. Berrangé]

On Wed, Apr 02, 2025 at 02:36:01PM +0200, Pierre-Samuel LE STANG wrote:
> Hello team, 
> 
> I'm facing the issue of windows instances not beeing able of retrieving
> the uuid because of smbios 3.0 (qemu 8.2 on debian openstack/libvirt).
> The instances are of pc-i440fx-8.2 machine type.
> 
> If I understand well since 8.1 qemu use a 64bit format for the smbios
> v3 which is not handle by windows OS.
> 
> I also found some commit about handling automatically the format by qemu
> on q35 machine type to resolve this bug startting to 9.0.0 version
> https://gitlab.com/qemu-project/qemu/-/issues/2008 
> 
> It seems forced to 64 bit on pc-i440fx-8.1 and above while forced to 32
> under.
> 
> Is there a reason to not handle it automatically on pc-i440fx machine
> type?

That is done since:

  commit 2c7c45b3d0ba097ac99bf4b9a13c6de1d7724032
  Author: Igor Mammedov <imammedo@redhat.com>
  Date:   Thu Mar 14 16:23:00 2024 +0100

    pc/q35: set SMBIOS entry point type to 'auto' by default
    
    Use smbios-entry-point-type='auto' for newer machine types as a workaround
    for Windows not detecting SMBIOS tables. Which makes QEMU pick SMBIOS tables
    based on configuration (with 2.x preferred and fallback to 3.x if the former
    isn't compatible with configuration)
    
    Default compat setting of smbios-entry-point-type after series
    for pc/q35 machines:
      * 9.0-newer: 'auto'
      * 8.1-8.2: '64'
      * 8.0-older: '32'

> Is it safe to keep it to 32 for machine type pc-i440fx-8.1 and above?

Once QEMU ships a particular machine type version, it is fixed and
we cannot change its defaults. Hence the "auto" choice of SMBIOS
entrypoint is only done for 9.0 or newer machine types.

With regards,
Daniel
-- 
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