Re: [PATCH 0/3] Make it possible to compile the x86 binaries without FDC

[Thomas Huth <thuth@redhat.com>]

On 25/04/2024 22.56, Philippe Mathieu-Daudé wrote:
> Hi Thomas,
> 
> On 25/4/24 20:43, Thomas Huth wrote:
>> For downstream versions of QEMU, we'd like to be able to compile QEMU
>> without the FDC code included (since it's not required for modern VMs
>> anymore and the FDC code has rather a bad reputation, see the VENOM CVE).
> 
> IIRC you still need to keep the i440fx+piix machine DS due to
> migration compatibility, right?
> 
> Are you able to migrate a VM booted with FDC to a non-FDC one?

Migration from a machine with FDC to one without is likely not possible. But 
that's also not the purpose of this series. It's about having the 
possibility to build a QEMU binary without FDC at all in case you don't have 
to support old machine types with FDC anymore.

>> The q35 machine can already be instantiated without FDC, but for being
>> able to link a binary without the FDC code, the Kconfig file needs some
>> tweaks and there are two spots in the pc code that directly call functions
>> from the FDC code - those need to be disabled via #ifdefs.
> 
> Is it useful to you to have q35 without FDC but i440fx+piix with?
> Or are you removing it from i440fx+piix due to shared code with q35?

I think it might get useful.

  Thomas