From: SeongJae Park sj@kernel.org
commit fc9be616bb8f3ed9cf560308f86904f5c06be205 upstream.
Persistent grants feature can be used only when both backend and the frontend supports the feature. The feature was always supported by 'blkback', but commit aac8a70db24b ("xen-blkback: add a parameter for disabling of persistent grants") has introduced a parameter for disabling it runtime.
To avoid the parameter be updated while being used by 'blkback', the commit caches the parameter into 'vbd->feature_gnt_persistent' in 'xen_vbd_create()', and then check if the guest also supports the feature and finally updates the field in 'connect_ring()'.
However, 'connect_ring()' could be called before 'xen_vbd_create()', so later execution of 'xen_vbd_create()' can wrongly overwrite 'true' to 'vbd->feature_gnt_persistent'. As a result, 'blkback' could try to use 'persistent grants' feature even if the guest doesn't support the feature.
This commit fixes the issue by moving the parameter value caching to 'xen_blkif_alloc()', which allocates the 'blkif'. Because the struct embeds 'vbd' object, which will be used by 'connect_ring()' later, this should be called before 'connect_ring()' and therefore this should be the right and safe place to do the caching.
Fixes: aac8a70db24b ("xen-blkback: add a parameter for disabling of persistent grants") Cc: stable@vger.kernel.org # 5.10.x Signed-off-by: Maximilian Heyne mheyne@amazon.de Signed-off-by: SeongJae Park sj@kernel.org Reviewed-by: Maximilian Heyne mheyne@amazon.de Reviewed-by: Juergen Gross jgross@suse.com Link: https://lore.kernel.org/r/20220715225108.193398-2-sj@kernel.org Signed-off-by: Juergen Gross jgross@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/block/xen-blkback/xenbus.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-)
--- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -157,6 +157,11 @@ static int xen_blkif_alloc_rings(struct return 0; }
+/* Enable the persistent grants feature. */ +static bool feature_persistent = true; +module_param(feature_persistent, bool, 0644); +MODULE_PARM_DESC(feature_persistent, "Enables the persistent grants feature"); + static struct xen_blkif *xen_blkif_alloc(domid_t domid) { struct xen_blkif *blkif; @@ -181,6 +186,8 @@ static struct xen_blkif *xen_blkif_alloc __module_get(THIS_MODULE); INIT_WORK(&blkif->free_work, xen_blkif_deferred_free);
+ blkif->vbd.feature_gnt_persistent = feature_persistent; + return blkif; }
@@ -472,12 +479,6 @@ static void xen_vbd_free(struct xen_vbd vbd->bdev = NULL; }
-/* Enable the persistent grants feature. */ -static bool feature_persistent = true; -module_param(feature_persistent, bool, 0644); -MODULE_PARM_DESC(feature_persistent, - "Enables the persistent grants feature"); - static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle, unsigned major, unsigned minor, int readonly, int cdrom) @@ -523,8 +524,6 @@ static int xen_vbd_create(struct xen_blk if (q && blk_queue_secure_erase(q)) vbd->discard_secure = true;
- vbd->feature_gnt_persistent = feature_persistent; - pr_debug("Successful creation of handle=%04x (dom=%u)\n", handle, blkif->domid); return 0;