KVM: PPC: Book3S HV: Introduce rmap to track nested guest mappings

When a host (L0) page which is mapped into a (L1) guest is in turn
mapped through to a nested (L2) guest we keep a reverse mapping (rmap)
so that these mappings can be retrieved later.

Whenever we create an entry in a shadow_pgtable for a nested guest we
create a corresponding rmap entry and add it to the list for the
L1 guest memslot at the index of the L1 guest page it maps. This means
at the L1 guest memslot we end up with lists of rmaps.

When we are notified of a host page being invalidated which has been
mapped through to a (L1) guest, we can then walk the rmap list for that
guest page, and find and invalidate all of the corresponding
shadow_pgtable entries.

In order to reduce memory consumption, we compress the information for
each rmap entry down to 52 bits -- 12 bits for the LPID and 40 bits
for the guest real page frame number -- which will fit in a single
unsigned long.  To avoid a scenario where a guest can trigger
unbounded memory allocations, we scan the list when adding an entry to
see if there is already an entry with the contents we need.  This can
occur, because we don't ever remove entries from the middle of a list.

A struct nested guest rmap is a list pointer and an rmap entry;
----------------
| next pointer |
----------------
| rmap entry   |
----------------

Thus the rmap pointer for each guest frame number in the memslot can be
either NULL, a single entry, or a pointer to a list of nested rmap entries.

gfn	 memslot rmap array
 	-------------------------
 0	| NULL			|	(no rmap entry)
 	-------------------------
 1	| single rmap entry	|	(rmap entry with low bit set)
 	-------------------------
 2	| list head pointer	|	(list of rmap entries)
 	-------------------------

The final entry always has the lowest bit set and is stored in the next
pointer of the last list entry, or as a single rmap entry.
With a list of rmap entries looking like;

-----------------	-----------------	-------------------------
| list head ptr	| ----> | next pointer	| ---->	| single rmap entry	|
-----------------	-----------------	-------------------------
			| rmap entry	|	| rmap entry		|
			-----------------	-------------------------

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 68 insertions, 1 deletions

diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
index 5496152f70e1..c2a9146ee016 100644
--- a/arch/powerpc/include/asm/kvm_book3s_64.h
+++ b/arch/powerpc/include/asm/kvm_book3s_64.h
@@ -53,6 +53,66 @@ struct kvm_nested_guest {
 	struct kvm_nested_guest *next;
 };
 
+/*
+ * We define a nested rmap entry as a single 64-bit quantity
+ * 0xFFF0000000000000	12-bit lpid field
+ * 0x000FFFFFFFFFF000	40-bit guest 4k page frame number
+ * 0x0000000000000001	1-bit  single entry flag
+ */
+#define RMAP_NESTED_LPID_MASK		0xFFF0000000000000UL
+#define RMAP_NESTED_LPID_SHIFT		(52)
+#define RMAP_NESTED_GPA_MASK		0x000FFFFFFFFFF000UL
+#define RMAP_NESTED_IS_SINGLE_ENTRY	0x0000000000000001UL
+
+/* Structure for a nested guest rmap entry */
+struct rmap_nested {
+	struct llist_node list;
+	u64 rmap;
+};
+
+/*
+ * for_each_nest_rmap_safe - iterate over the list of nested rmap entries
+ *			     safe against removal of the list entry or NULL list
+ * @pos:	a (struct rmap_nested *) to use as a loop cursor
+ * @node:	pointer to the first entry
+ *		NOTE: this can be NULL
+ * @rmapp:	an (unsigned long *) in which to return the rmap entries on each
+ *		iteration
+ *		NOTE: this must point to already allocated memory
+ *
+ * The nested_rmap is a llist of (struct rmap_nested) entries pointed to by the
+ * rmap entry in the memslot. The list is always terminated by a "single entry"
+ * stored in the list element of the final entry of the llist. If there is ONLY
+ * a single entry then this is itself in the rmap entry of the memslot, not a
+ * llist head pointer.
+ *
+ * Note that the iterator below assumes that a nested rmap entry is always
+ * non-zero.  This is true for our usage because the LPID field is always
+ * non-zero (zero is reserved for the host).
+ *
+ * This should be used to iterate over the list of rmap_nested entries with
+ * processing done on the u64 rmap value given by each iteration. This is safe
+ * against removal of list entries and it is always safe to call free on (pos).
+ *
+ * e.g.
+ * struct rmap_nested *cursor;
+ * struct llist_node *first;
+ * unsigned long rmap;
+ * for_each_nest_rmap_safe(cursor, first, &rmap) {
+ *	do_something(rmap);
+ *	free(cursor);
+ * }
+ */
+#define for_each_nest_rmap_safe(pos, node, rmapp)			       \
+	for ((pos) = llist_entry((node), typeof(*(pos)), list);		       \
+	     (node) &&							       \
+	     (*(rmapp) = ((RMAP_NESTED_IS_SINGLE_ENTRY & ((u64) (node))) ?     \
+			  ((u64) (node)) : ((pos)->rmap))) &&		       \
+	     (((node) = ((RMAP_NESTED_IS_SINGLE_ENTRY & ((u64) (node))) ?      \
+			 ((struct llist_node *) ((pos) = NULL)) :	       \
+			 (pos)->list.next)), true);			       \
+	     (pos) = llist_entry((node), typeof(*(pos)), list))
+
 struct kvm_nested_guest *kvmhv_get_nested(struct kvm *kvm, int l1_lpid,
 					  bool create);
 void kvmhv_put_nested(struct kvm_nested_guest *gp);
@@ -551,7 +611,14 @@ static inline void copy_to_checkpoint(struct kvm_vcpu *vcpu)
 
 extern int kvmppc_create_pte(struct kvm *kvm, pgd_t *pgtable, pte_t pte,
 			     unsigned long gpa, unsigned int level,
-			     unsigned long mmu_seq, unsigned int lpid);
+			     unsigned long mmu_seq, unsigned int lpid,
+			     unsigned long *rmapp, struct rmap_nested **n_rmap);
+extern void kvmhv_insert_nest_rmap(struct kvm *kvm, unsigned long *rmapp,
+				   struct rmap_nested **n_rmap);
+extern void kvmhv_remove_nest_rmap_range(struct kvm *kvm,
+				struct kvm_memory_slot *memslot,
+				unsigned long gpa, unsigned long hpa,
+				unsigned long nbytes);
 
 #endif /* CONFIG_KVM_BOOK3S_HV_POSSIBLE */