s390/uv: add destroy page call

We don't need to export pages if we destroy the VM configuration
afterwards anyway. Instead we can destroy the page which will zero it
and then make it accessible to the host.

Destroying is about twice as fast as the export.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Link: https://lore.kernel.org/kvm/20200907124700.10374-2-frankja@linux.ibm.com/
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/asm/uv.h

@@ -33,6 +33,7 @@
 #define UVC_CMD_DESTROY_SEC_CPU		0x0121
 #define UVC_CMD_CONV_TO_SEC_STOR	0x0200
 #define UVC_CMD_CONV_FROM_SEC_STOR	0x0201
+#define UVC_CMD_DESTR_SEC_STOR		0x0202
 #define UVC_CMD_SET_SEC_CONF_PARAMS	0x0300
 #define UVC_CMD_UNPACK_IMG		0x0301
 #define UVC_CMD_VERIFY_IMG		0x0302
@@ -344,6 +345,7 @@ static inline int is_prot_virt_host(void)
 }
 
 int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb);
+int uv_destroy_page(unsigned long paddr);
 int uv_convert_from_secure(unsigned long paddr);
 int gmap_convert_to_secure(struct gmap *gmap, unsigned long gaddr);
 
@@ -354,6 +356,11 @@ void adjust_to_uv_max(unsigned long *vmax);
 static inline void setup_uv(void) {}
 static inline void adjust_to_uv_max(unsigned long *vmax) {}
 
+static inline int uv_destroy_page(unsigned long paddr)
+{
+	return 0;
+}
+
 static inline int uv_convert_from_secure(unsigned long paddr)
 {
 	return 0;

arch/s390/kernel/uv.c

@@ -118,6 +118,26 @@ static int uv_pin_shared(unsigned long paddr)
 	return 0;
 }
 
+/*
+ * Requests the Ultravisor to destroy a guest page and make it
+ * accessible to the host. The destroy clears the page instead of
+ * exporting.
+ *
+ * @paddr: Absolute host address of page to be destroyed
+ */
+int uv_destroy_page(unsigned long paddr)
+{
+	struct uv_cb_cfs uvcb = {
+		.header.cmd = UVC_CMD_DESTR_SEC_STOR,
+		.header.len = sizeof(uvcb),
+		.paddr = paddr
+	};
+
+	if (uv_call(0, (u64)&uvcb))
+		return -EINVAL;
+	return 0;
+}
+
 /*
  * Requests the Ultravisor to encrypt a guest page and make it
  * accessible to the host for paging (export).

arch/s390/mm/gmap.c

@@ -2679,7 +2679,7 @@ static int __s390_reset_acc(pte_t *ptep, unsigned long addr,
 	pte_t pte = READ_ONCE(*ptep);
 
 	if (pte_present(pte))
-		WARN_ON_ONCE(uv_convert_from_secure(pte_val(pte) & PAGE_MASK));
+		WARN_ON_ONCE(uv_destroy_page(pte_val(pte) & PAGE_MASK));
 	return 0;
 }