Re: [PATCH 3/7] KVM: arm64: Remove list_head from hyp_page

On Tuesday 01 Jun 2021 at 15:38:22 (+0100), Marc Zyngier wrote:

On Thu, 27 May 2021 13:51:30 +0100,
Quentin Perret [off-list ref] wrote:

quoted

+/*
+ * Pages that are available for allocation are tracked in free-lists, so we use
+ * the pages themselves to store the list nodes to avoid wasting space. As the
+ * allocator always returns zeroed pages (which are zeroed on the hyp_put_page()
+ * path to optimize allocation speed), we also need to clean-up the list node in
+ * each page when we take it out of the list.
+ */
+static inline void page_remove_from_list(struct hyp_page *p)
+{
+	struct list_head *node = (struct list_head *)hyp_page_to_virt(p);

Nit: How about changing hyp_page_to_virt() so that it returns a
convenient 'void *', and get rid of the ugly casts?

It should already return void *, but I kind of liked the explicit cast
here for documentation purpose. We're turning a 'random' piece of unused
memory into a typed object, so that felt like a useful annotation. Happy
to get rid of it though.

quoted

+
+	__list_del_entry(node);
+	memset(node, 0, sizeof(*node));
+}
+
+static inline void page_add_to_list(struct hyp_page *p, struct list_head *head)
+{
+	struct list_head *node = (struct list_head *)hyp_page_to_virt(p);
+
+	INIT_LIST_HEAD(node);
+	list_add_tail(node, head);
+}
+
+static inline struct hyp_page *node_to_page(struct list_head *node)
+{
+	return (struct hyp_page *)hyp_virt_to_page(node);

Why is this cast necessary? If I'm not mistaken, hyp_vmemmap is
already cast as a 'struct hyp_page *', so hyp_virt_to_page() should
return the same type.

Right, that one is totally unnecessary, I'll remove.

Cheers,
Quentin

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