Re: [PATCH] arm64/defconfig: Restore built-in 9P rootfs support

[Anshuman Khandual]

On 16/07/26 5:01 PM, Arnd Bergmann wrote:
> On Thu, Jul 16, 2026, at 13:01, Krzysztof Kozlowski wrote:
>> On 16/07/2026 12:02, Anshuman Khandual wrote:
>>> Commit d521c4ca039f ("arm64: defconfig: Switch Ethernet drivers to modules")
>>> had changed 9P and virtio-9P support from built-in to modular instead. This
>>> breaks simple kvmtool boots using a 9P root filesystem without an initramfs
>>> , because the kernel must mount root filesystem before it can load the 9P
>>
>>
>> And that commit explained you must use initramfs. Nothing got broken,
>> because there was never a promise that a recent, virtualized environment
>> must work on defconfig without initramfs.
>>
>> You fully control your software, so just build initramfs which is
>> absolutely trivial and we all moved on to that for arm64 long time ago.
> 
> I still regularly boot KVM guests on arm64 without an initramfs,

Actually that is a very normal use case particularly with KVM tool.
> but I just use 'make kvm_guest.config', which turns on all the
> commonly used virtio drivers as built-in. I wouldn't call
> 9pfs root trivial without initramfs, configuring 9p built-in
> is already complicated enough.

Alright - fair enough.
> 
> So I agree we don't need this patch, but there is a trivial
> workaround for Anshuman in case he wants to avoid doing this.
The following sequence does indeed solve this problem for now.

make mrproper
make defconfig
make kvm_guest.config