On Tue, Jan 06, 2026 at 02:32:12PM +0000, Quentin Perret wrote:

On Monday 05 Jan 2026 at 15:49:10 (+0000), Will Deacon wrote:

quoted

The MMU notifiers are registered by kvm_init_mmu_notifier() only after
kvm_arch_init_vm() has returned successfully. Since the latter function
initialises the 'kvm->arch.mmu.pgt' pointer (and allocates the VM handle
when pKVM is enabled), the initialisation checks in the MMU notifiers
are not required.

It took me a while to remember, but I think these checks are needed for
the free path rather than init. In particular, the doc for
mmu_notifier_ops::release() (from which we free the pgt) says that it
"can run concurrently with other mmu notifier" (see mmu_notifier.h), which
is fun.

Had you considered that path? If so, probably worth expanding in the
commit description why this is safe?

Urgh....

Let me get back to you on that :)

Will