Remove redundant code in mshv_vtl_main.c

[namancse]

No description provided.

[Copilot]

Pull request overview

This PR changes how /dev/mshv_vtl_low page faults determine whether a PFN belongs to an mshv_vtl-owned dev_pagemap, aiming to avoid a race where get_dev_pagemap() can observe a pgmap before the vmemmap/struct page backing is fully initialized.

Changes:

• Introduces a driver-owned RCU-published list of “ready” PFN ranges, populated only after devm_memremap_pages() completes.
• Updates the low-fault PFN resolution path to consult the published ranges and then validate ownership via page_pgmap().
• Adds module-exit teardown to unlink and free the published range metadata.

Comments suppressed due to low confidence (2)

drivers/hv/mshv_vtl_main.c:1181

• mshv_vtl_low_ranges is traversed under RCU, but struct mshv_vtl_low_range currently lacks an rcu_head, which makes it hard to safely free entries via kfree_rcu() (and the current exit path reuses the list pointers before a grace period, see other comment). Add an rcu_head to the node so deletion can defer freeing without touching the forward link that RCU readers may still be using.

struct mshv_vtl_low_range {
	struct list_head list;
	unsigned long start_pfn;
	unsigned long end_pfn;	/* exclusive */
};

drivers/hv/mshv_vtl_main.c:4123

• The module-exit cleanup deletes entries with list_del_rcu() and then immediately reuses the same list_head by linking it into the local stale list. This violates list_del_rcu()'s requirement to keep the forward pointer intact for in-flight list_for_each_entry_rcu() readers, and can corrupt RCU traversal before synchronize_rcu() runs. Prefer deleting with list_del_rcu() and deferring the free via kfree_rcu() (after adding an rcu_head to the node), eliminating the need to relink into stale/synchronize_rcu().

	spin_lock(&mshv_vtl_low_ranges_lock);
	list_for_each_entry_safe(r, tmp, &mshv_vtl_low_ranges, list) {
		list_del_rcu(&r->list);
		list_add(&r->list, &stale);
	}
	spin_unlock(&mshv_vtl_low_ranges_lock);
	synchronize_rcu();
	list_for_each_entry_safe(r, tmp, &stale, list)
		kfree(r);

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