Re: [RFC PATCH] x86/xen: Consider Xen PVH support in CONFIG_XEN_PVHVM

["Jürgen Groß" <jgross@suse.com>]

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On 24.02.26 12:14, Roger Pau Monné wrote:
> On Tue, Feb 24, 2026 at 10:51:35AM +0000, Teddy Astie wrote:
>> It's currently possible to build Linux with CONFIG_PVH|CONFIG_XEN_PVHVM
>> and no CONFIG_XEN_PVH. That leads to inconsistent kernels that fails with
>> "Missing xen PVH initialization" when booting using PVH boot method or
>> display various errors and fail to initialize Xen PV drivers when booting
>> with PVH-GRUB.
>>
>>      platform_pci_unplug: Xen Platform PCI: unrecognised magic value
>>      ...
>>      # modprobe xen-blkfront
>>      modprobe: ERROR: could not insert 'xen_blkfront': No such device
>>      # modprobe xen-netfront
>>      modprobe: ERROR: could not insert 'xen_netfront': No such device
>>
>> When built without CONFIG_XEN_PVH, PVH-specific logic is disabled, hence when
>> booting with e.g PVH-OVMF, Linux assumes we are a HVM guest, even when we aren't
>> actually one (in the "with HVM emulated devices" sense).
>>
>> As it is actually possible to boot Xen PVH without CONFIG_PVH; and that most
>> Xen-related logic exist within CONFIG_XEN_PVHVM; consider PVH guests support
>> within CONFIG_XEN_PVHVM instead of CONFIG_XEN_PVH.
> 
> So the current CONFIG_PVH selection done by CONFIG_XEN_PVH is moot?

No, it isn't.

CONFIG_PVH is the common base needed for Xen and KVM guests to be able to
run in PVH mode.

> 
>> Keep CONFIG_XEN_PVH as a shortcut to enable PVH boot, ACPI support and PVHVM.
>>
>> Signed-off-by: Teddy Astie <teddy.astie@vates.tech>
>> ---
>> Cc: Juergen Gross <jgross@suse.com>
>> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>> Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>
>> A tentative patch, I'm not sure of the way of dealing with the KConfig part,
>> keeping CONFIG_XEN_PVH as a shortcut is interesting, but there may be other
>> options.
>>
>> There are widespreadly used Linux distributions that have a similar configuration
>> to this one, thus exhibit this issue i.e fail to boot.
> 
> Do you know the underlying cause of not enabling CONFIG_XEN_PVH?  Is
> the default set to n on the defconfig?  Or are distros specifically
> disabling this option on purpose?
> 
> It seems like a step backwards to merge this into some bigger generic
> option, we always try to fine-grain as much as possible.
> 
> Maybe you could introduce XEN_HVM meta option, that selects both PVHVM
> and PVH?
No, please don't use "HVM" for that purpose.

If anything I'd set the CONFIG_XEN_PVH default to that of CONFIG_XEN_PVHVM.


Juergen

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