Subject: Re: [PATCH mm-unstable v1 1/5] mm/kvm: add mmu_notifier_test_clear_young()

From: Sean Christopherson <[email-masked]>
Date: Thu, 23 Feb 2023 09:13:58 -0800

On Thu, Feb 16, 2023, Yu Zhao wrote:
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 9c60384b5ae0..1b465df4a93d 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -875,6 +875,63 @@ static int kvm_mmu_notifier_clear_young(struct mmu_notifier *mn,
>  	return kvm_handle_hva_range_no_flush(mn, start, end, kvm_age_gfn);
>  }
>  
> +static bool kvm_test_clear_young(struct kvm *kvm, unsigned long start,
> +				 unsigned long end, unsigned long *bitmap)
> +{
> +	int i;
> +	int key;
> +	bool success = true;
> +
> +	trace_kvm_age_hva(start, end);
> +
> +	key = srcu_read_lock(&kvm->srcu);
> +
> +	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> +		struct interval_tree_node *node;
> +		struct kvm_memslots *slots = __kvm_memslots(kvm, i);
> +
> +		kvm_for_each_memslot_in_hva_range(node, slots, start, end - 1) {
> +			gfn_t lsb_gfn;
> +			unsigned long hva_start, hva_end;
> +			struct kvm_gfn_range range = {
> +				.slot = container_of(node, struct kvm_memory_slot,
> +						     hva_node[slots->node_idx]),
> +			};
> +
> +			hva_start = max(start, range.slot->userspace_addr);
> +			hva_end = min(end - 1, range.slot->userspace_addr +
> +					       range.slot->npages * PAGE_SIZE - 1);
> +
> +			range.start = hva_to_gfn_memslot(hva_start, range.slot);
> +			range.end = hva_to_gfn_memslot(hva_end, range.slot) + 1;
> +
> +			if (WARN_ON_ONCE(range.end <= range.start))
> +				continue;

Extend __kvm_handle_hva_range() instead of copy-pasting.  At a very quick glance,
I believe all that is needed is (minus sanity checks):

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d255964ec331..3296ae2cf6fa 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -544,6 +544,7 @@ struct kvm_hva_range {
        hva_handler_t handler;
        on_lock_fn_t on_lock;
        on_unlock_fn_t on_unlock;
+       bool lockless;
        bool flush_on_ret;
        bool may_block;
 };
@@ -616,7 +617,7 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
                        gfn_range.end = hva_to_gfn_memslot(hva_end + PAGE_SIZE - 1, slot);
                        gfn_range.slot = slot;
 
-                       if (!locked) {
+                       if (!range->lockless && !locked) {
                                locked = true;
                                KVM_MMU_LOCK(kvm);
                                if (!IS_KVM_NULL_FN(range->on_lock))

> +
> +			/* see the comments on the generic kvm_arch_has_test_clear_young() */
> +			lsb_gfn = hva_to_gfn_memslot(end - 1, range.slot);
> +
> +			success = kvm_arch_test_clear_young(kvm, &range, lsb_gfn, bitmap);
> +			if (!success)
> +				break;
> +		}
> +	}
> +
> +	srcu_read_unlock(&kvm->srcu, key);
> +
> +	return success;
> +}