Patch "virtio-mem: check if the config changed before fake offlining memory" has been added to the 6.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    virtio-mem: check if the config changed before fake offlining memory

to the 6.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     virtio-mem-check-if-the-config-changed-before-fake-o.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 114ea675fe14f87a040e0cf7a591da605f727dda
Author: David Hildenbrand <david@xxxxxxxxxx>
Date:   Thu Jul 13 16:55:51 2023 +0200

    virtio-mem: check if the config changed before fake offlining memory
    
    [ Upstream commit f55484fd7be923b740e8e1fc304070ba53675cb4 ]
    
    If we repeatedly fail to fake offline memory to unplug it, we won't be
    sending any unplug requests to the device. However, we only check if the
    config changed when sending such (un)plug requests.
    
    We could end up trying for a long time to unplug memory, even though
    the config changed already and we're not supposed to unplug memory
    anymore. For example, the hypervisor might detect a low-memory situation
    while unplugging memory and decide to replug some memory. Continuing
    trying to unplug memory in that case can be problematic.
    
    So let's check on a more regular basis.
    
    Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
    Message-Id: <20230713145551.2824980-5-david@xxxxxxxxxx>
    Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index a5cf92e3e5af2..fa5226c198cc6 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -1189,7 +1189,8 @@ static void virtio_mem_fake_online(unsigned long pfn, unsigned long nr_pages)
  * Try to allocate a range, marking pages fake-offline, effectively
  * fake-offlining them.
  */
-static int virtio_mem_fake_offline(unsigned long pfn, unsigned long nr_pages)
+static int virtio_mem_fake_offline(struct virtio_mem *vm, unsigned long pfn,
+				   unsigned long nr_pages)
 {
 	const bool is_movable = is_zone_movable_page(pfn_to_page(pfn));
 	int rc, retry_count;
@@ -1202,6 +1203,14 @@ static int virtio_mem_fake_offline(unsigned long pfn, unsigned long nr_pages)
 	 * some guarantees.
 	 */
 	for (retry_count = 0; retry_count < 5; retry_count++) {
+		/*
+		 * If the config changed, stop immediately and go back to the
+		 * main loop: avoid trying to keep unplugging if the device
+		 * might have decided to not remove any more memory.
+		 */
+		if (atomic_read(&vm->config_changed))
+			return -EAGAIN;
+
 		rc = alloc_contig_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE,
 					GFP_KERNEL);
 		if (rc == -ENOMEM)
@@ -1951,7 +1960,7 @@ static int virtio_mem_sbm_unplug_sb_online(struct virtio_mem *vm,
 	start_pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
 			     sb_id * vm->sbm.sb_size);
 
-	rc = virtio_mem_fake_offline(start_pfn, nr_pages);
+	rc = virtio_mem_fake_offline(vm, start_pfn, nr_pages);
 	if (rc)
 		return rc;
 
@@ -2149,7 +2158,7 @@ static int virtio_mem_bbm_offline_remove_and_unplug_bb(struct virtio_mem *vm,
 		if (!page)
 			continue;
 
-		rc = virtio_mem_fake_offline(pfn, PAGES_PER_SECTION);
+		rc = virtio_mem_fake_offline(vm, pfn, PAGES_PER_SECTION);
 		if (rc) {
 			end_pfn = pfn;
 			goto rollback;