s390/mm: add shadow gmap support

For a nested KVM guest the outer KVM host needs to create shadow
page tables for the nested guest. This patch adds the basic support
to the guest address space (gmap) code.

For each guest address space the inner KVM host creates, the first
outer KVM host needs to create shadow page tables. The address space
is identified by the ASCE loaded into the control register 1 at the
time the inner SIE instruction for the second nested KVM guest is
executed. The outer KVM host creates the shadow tables starting with
the table identified by the ASCE on a on-demand basis. The outer KVM
host will get repeated faults for all the shadow tables needed to
run the second KVM guest.

While a shadow page table for the second KVM guest is active the access
to the origin region, segment and page tables needs to be restricted
for the first KVM guest. For region and segment and page tables the first
KVM guest may read the memory, but write attempt has to lead to an
unshadow.  This is done using the page invalid and read-only bits in the
page table of the first KVM guest. If the first guest re-accesses one of
the origin pages of a shadow, it gets a fault and the affected parts of
the shadow page table hierarchy needs to be removed again.

PGSTE tables don't have to be shadowed, as all interpretation assist can't
deal with the invalid bits in the shadow pte being set differently than
the original ones provided by the first KVM guest.

Many bug fixes and improvements by David Hildenbrand.

Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

1 files changed, 51 insertions, 1 deletions

diff --git a/arch/s390/include/asm/gmap.h b/arch/s390/include/asm/gmap.h
index e69853ce55da..58e65ee5b2d2 100644
--- a/arch/s390/include/asm/gmap.h
+++ b/arch/s390/include/asm/gmap.h
@@ -10,6 +10,7 @@
 
 /**
  * struct gmap_struct - guest address space
+ * @list: list head for the mm->context gmap list
  * @crst_list: list of all crst tables used in the guest address space
  * @mm: pointer to the parent mm_struct
  * @guest_to_host: radix tree with guest to host address translation
@@ -19,6 +20,13 @@
  * @table: pointer to the page directory
  * @asce: address space control element for gmap page table
  * @pfault_enabled: defines if pfaults are applicable for the guest
+ * @host_to_rmap: radix tree with gmap_rmap lists
+ * @children: list of shadow gmap structures
+ * @pt_list: list of all page tables used in the shadow guest address space
+ * @shadow_lock: spinlock to protect the shadow gmap list
+ * @parent: pointer to the parent gmap for shadow guest address spaces
+ * @orig_asce: ASCE for which the shadow page table has been created
+ * @removed: flag to indicate if a shadow guest address space has been removed
  */
 struct gmap {
 	struct list_head list;
@@ -33,9 +41,33 @@ struct gmap {
 	unsigned long asce_end;
 	void *private;
 	bool pfault_enabled;
+	/* Additional data for shadow guest address spaces */
+	struct radix_tree_root host_to_rmap;
+	struct list_head children;
+	struct list_head pt_list;
+	spinlock_t shadow_lock;
+	struct gmap *parent;
+	unsigned long orig_asce;
+	bool removed;
 };
 
 /**
+ * struct gmap_rmap - reverse mapping for shadow page table entries
+ * @next: pointer to next rmap in the list
+ * @raddr: virtual rmap address in the shadow guest address space
+ */
+struct gmap_rmap {
+	struct gmap_rmap *next;
+	unsigned long raddr;
+};
+
+#define gmap_for_each_rmap(pos, head) \
+	for (pos = (head); pos; pos = pos->next)
+
+#define gmap_for_each_rmap_safe(pos, n, head) \
+	for (pos = (head); n = pos ? pos->next : NULL, pos; pos = n)
+
+/**
  * struct gmap_notifier - notify function block for page invalidation
  * @notifier_call: address of callback function
  */
@@ -46,6 +78,11 @@ struct gmap_notifier {
 			      unsigned long end);
 };
 
+static inline int gmap_is_shadow(struct gmap *gmap)
+{
+	return !!gmap->parent;
+}
+
 struct gmap *gmap_create(struct mm_struct *mm, unsigned long limit);
 void gmap_remove(struct gmap *gmap);
 struct gmap *gmap_get(struct gmap *gmap);
@@ -64,9 +101,22 @@ void gmap_discard(struct gmap *, unsigned long from, unsigned long to);
 void __gmap_zap(struct gmap *, unsigned long gaddr);
 void gmap_unlink(struct mm_struct *, unsigned long *table, unsigned long vmaddr);
 
+int gmap_read_table(struct gmap *gmap, unsigned long gaddr, unsigned long *val);
+
+struct gmap *gmap_shadow(struct gmap *parent, unsigned long asce);
+int gmap_shadow_r2t(struct gmap *sg, unsigned long saddr, unsigned long r2t);
+int gmap_shadow_r3t(struct gmap *sg, unsigned long saddr, unsigned long r3t);
+int gmap_shadow_sgt(struct gmap *sg, unsigned long saddr, unsigned long sgt);
+int gmap_shadow_pgt(struct gmap *sg, unsigned long saddr, unsigned long pgt);
+int gmap_shadow_pgt_lookup(struct gmap *sg, unsigned long saddr,
+			   unsigned long *pgt, int *dat_protection);
+int gmap_shadow_page(struct gmap *sg, unsigned long saddr,
+		     unsigned long paddr, int write);
+
 void gmap_register_pte_notifier(struct gmap_notifier *);
 void gmap_unregister_pte_notifier(struct gmap_notifier *);
-void gmap_pte_notify(struct mm_struct *, unsigned long addr, pte_t *);
+void gmap_pte_notify(struct mm_struct *, unsigned long addr, pte_t *,
+		     unsigned long bits);
 
 int gmap_mprotect_notify(struct gmap *, unsigned long start,
 			 unsigned long len, int prot);