[PATCH v2 08/13] vfio/pci: protect cap/ecap_perm bits alloc/free with atomic op

Liu Yi L
2019-09-06T08:18:18Z

There is a case in which cap_perms and ecap_perms can be reallocated
by different modules. e.g. the vfio-mdev-pci sample driver. To secure
the initialization of cap_perms and ecap_perms, this patch adds an
atomic variable to track the user of cap/ecap_perms bits. First caller
of vfio_pci_init_perm_bits() will initialize the bits. While the last
caller of vfio_pci_uninit_perm_bits() will free the bits.

Cc: Kevin Tian <kevin.tian@intel.com>
Cc: Lu Baolu <baolu.lu@linux.intel.com>
Suggested-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
---
drivers/vfio/pci/vfio_pci_config.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
index f0891bd..1b3e6e5 100644
--- a/drivers/vfio/pci/vfio_pci_config.c
+++ b/drivers/vfio/pci/vfio_pci_config.c
@@ -992,11 +992,17 @@ static int __init init_pci_ext_cap_pwr_perm(struct perm_bits *perm)
return 0;
}

+/* Track the user number of the cap/ecap perm_bits */
+atomic_t vfio_pci_perm_bits_users = ATOMIC_INIT(0);
+
/*
* Initialize the shared permission tables
*/
void vfio_pci_uninit_perm_bits(void)
{
+ if (atomic_dec_return(&vfio_pci_perm_bits_users))
+ return;
+
free_perm_bits(&cap_perms[PCI_CAP_ID_BASIC]);

free_perm_bits(&cap_perms[PCI_CAP_ID_PM]);
@@ -1013,6 +1019,9 @@ int __init vfio_pci_init_perm_bits(void)
{
int ret;

+ if (atomic_inc_return(&vfio_pci_perm_bits_users) != 1)
+ return 0;
+
/* Basic config space */
ret = init_pci_cap_basic_perm(&cap_perms[PCI_CAP_ID_BASIC]);

--
2.7.4