s390/uv: gmap_make_secure() cleanups for further changes

Let's factor out handling of LRU cache draining and convert the if-else
chain to a switch-case.

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20240508182955.358628-3-david@redhat.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
index 016993e9eb72f670ea7673944a8af955f4f97edd..25fe28d189df088eb1863580db5c8edd0c3fc789 100644 (file)
--- a/arch/s390/kernel/uv.c
+++ b/arch/s390/kernel/uv.c
@@ -266,6 +266,36 @@ static bool should_export_before_import(struct uv_cb_header *uvcb, struct mm_str
        return atomic_read(&mm->context.protected_count) > 1;
 }
 
+/*
+ * Drain LRU caches: the local one on first invocation and the ones of all
+ * CPUs on successive invocations. Returns "true" on the first invocation.
+ */
+static bool drain_lru(bool *drain_lru_called)
+{
+       /*
+        * If we have tried a local drain and the folio refcount
+        * still does not match our expected safe value, try with a
+        * system wide drain. This is needed if the pagevecs holding
+        * the page are on a different CPU.
+        */
+       if (*drain_lru_called) {
+               lru_add_drain_all();
+               /* We give up here, don't retry immediately. */
+               return false;
+       }
+       /*
+        * We are here if the folio refcount does not match the
+        * expected safe value. The main culprits are usually
+        * pagevecs. With lru_add_drain() we drain the pagevecs
+        * on the local CPU so that hopefully the refcount will
+        * reach the expected safe value.
+        */
+       lru_add_drain();
+       *drain_lru_called = true;
+       /* The caller should try again immediately */
+       return true;
+}
+
 /*
  * Requests the Ultravisor to make a page accessible to a guest.
  * If it's brought in the first time, it will be cleared. If
@@ -275,7 +305,7 @@ static bool should_export_before_import(struct uv_cb_header *uvcb, struct mm_str
 int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb)
 {
        struct vm_area_struct *vma;
-       bool local_drain = false;
+       bool drain_lru_called = false;
        spinlock_t *ptelock;
        unsigned long uaddr;
        struct folio *folio;
@@ -331,37 +361,21 @@ unlock:
 out:
        mmap_read_unlock(gmap->mm);
 
-       if (rc == -EAGAIN) {
+       switch (rc) {
+       case -EAGAIN:
                /*
                 * If we are here because the UVC returned busy or partial
                 * completion, this is just a useless check, but it is safe.
                 */
                folio_wait_writeback(folio);
                folio_put(folio);
-       } else if (rc == -EBUSY) {
-               /*
-                * If we have tried a local drain and the folio refcount
-                * still does not match our expected safe value, try with a
-                * system wide drain. This is needed if the pagevecs holding
-                * the page are on a different CPU.
-                */
-               if (local_drain) {
-                       lru_add_drain_all();
-                       /* We give up here, and let the caller try again */
-                       return -EAGAIN;
-               }
-               /*
-                * We are here if the folio refcount does not match the
-                * expected safe value. The main culprits are usually
-                * pagevecs. With lru_add_drain() we drain the pagevecs
-                * on the local CPU so that hopefully the refcount will
-                * reach the expected safe value.
-                */
-               lru_add_drain();
-               local_drain = true;
-               /* And now we try again immediately after draining */
-               goto again;
-       } else if (rc == -ENXIO) {
+               return -EAGAIN;
+       case -EBUSY:
+               /* Additional folio references. */
+               if (drain_lru(&drain_lru_called))
+                       goto again;
+               return -EAGAIN;
+       case -ENXIO:
                if (gmap_fault(gmap, gaddr, FAULT_FLAG_WRITE))
                        return -EFAULT;
                return -EAGAIN;