Re: [PATCH v4 4/7] KVM: Move MMU lock acquisition for test/clear_young to architecture

[Sean Christopherson]

On Wed, May 29, 2024, James Houghton wrote:
> For implementation mmu_notifier_{test,clear}_young, the KVM memslot
> walker used to take the MMU lock for us. Now make the architectures
> take it themselves.

Hmm, *forcing* architectures to take mmu_lock is a step backwards.  Rather than
add all of this churn, what about adding CONFIG_KVM_MMU_NOTIFIER_LOCKLESS, e.g.

static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier 
*mn,
                                                         unsigned long start,
                                                         unsigned long end,
                                                         gfn_handler_t handler)
{
        struct kvm *kvm = mmu_notifier_to_kvm(mn);
        const struct kvm_mmu_notifier_range range = {
                .start          = start,
                .end            = end,
                .handler        = handler,
                .on_lock        = (void *)kvm_null_fn,
                .flush_on_ret   = false,
                .may_block      = false,
                .lockless       = IS_ENABLED(CONFIG_KVM_MMU_NOTIFIER_LOCKLESS),
        };

        return __kvm_handle_hva_range(kvm, &range).ret;
}