[PATCH v3 02/10] s390/uv: gmap_make_secure() cleanups for further changes

David Hildenbrand
2024-05-08T18:30:09Z

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>
---
arch/s390/kernel/uv.c | 66 ++++++++++++++++++++++++++-----------------
1 file changed, 40 insertions(+), 26 deletions(-)

diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
index 016993e9eb72..25fe28d189df 100644
--- 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 @@ int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb)
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;
--
2.45.0