Commit ade6c6c8 authored by SeongJae Park's avatar SeongJae Park Committed by Zheng Zengkai
Browse files

xen-blkback: fix persistent grants negotiation 

stable inclusion
from stable-v5.10.137
commit 9e840884527667685f6ade040b1b79006157df07
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60PLB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9e840884527667685f6ade040b1b79006157df07



--------------------------------

commit fc9be616 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 aac8a70d ("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: aac8a70d ("xen-blkback: add a parameter for disabling of persistent grants")
Cc: <stable@vger.kernel.org> # 5.10.x
Signed-off-by: default avatarMaximilian Heyne <mheyne@amazon.de>
Signed-off-by: default avatarSeongJae Park <sj@kernel.org>
Reviewed-by: default avatarMaximilian Heyne <mheyne@amazon.de>
Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20220715225108.193398-2-sj@kernel.org


Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarZheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: default avatarWei Li <liwei391@huawei.com>
parent ce9e3ba2

drivers/block/xen-blkback/xenbus.c

+7 −8
Original line number Diff line number Diff line
@@ -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)
@@ -523,8 +524,6 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle, 
	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;