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

On Tuesday 01 Jun 2021 at 18:41:49 (+0100), Marc Zyngier wrote:

On Tue, 01 Jun 2021 16:48:06 +0100,
Quentin Perret [off-list ref] wrote:

quoted

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

quoted

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.

My expectations were that using hyp_page_to_virt() already serves as a
pretty big warning that we're doing something unusual.

I guess that if we want to be really careful about those, we should
then be consistent and make it return a uintptr_t (or unsigned long)
instead, actively making use of the cast, consistently, everywhere.

Right, so I'd prefer keeping it void * for consistency with the EL1
equivalent -- much of this aims to be API compatible with the Linux
stuff. I'll get rid of the cast and post a v2 shortly.

Cheers,
Quentin

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