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authorSeongJae Park <sj@kernel.org>2022-07-15 22:51:06 +0000
committerJuergen Gross <jgross@suse.com>2022-08-12 12:13:46 +0200
commitfc9be616bb8f3ed9cf560308f86904f5c06be205 (patch)
tree5b21db057d98fe9519d8becea175d12c89c0f956 /drivers
parentb1c3497e604ddccea5af4071831ed0e4680fb35e (diff)
xen-blkback: fix persistent grants negotiation
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>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/block/xen-blkback/xenbus.c15
1 files changed, 7 insertions, 8 deletions
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 97de13b14175..16c6785d260c 100644
--- 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 xen_blkif *blkif)
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(domid_t domid)
__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)
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)
@@ -520,8 +521,6 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
if (bdev_max_secure_erase_sectors(bdev))
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;

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