Re: [PATCH 02/30] KVM: arm64: Remove redundant 'pgt' pointer checks from MMU notifiers

Will Deacon
2026-01-09T14:31:59Z

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:
> > 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