On Thu, 5 Sep 2019 15:59:25 +0800 Liu Yi L <yi.l....@intel.com> wrote:
> 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. Yes, but it still allows races; we're not really protecting the data. If driver A begins freeing the shared data in the uninit path, driver B could start allocating shared data in the init path and we're left with either use after free issues or memory leaks. Probably better to hold a semaphore around the allocation/free and a non-atomic for reference counting. Thanks, Alex > Cc: Kevin Tian <kevin.t...@intel.com> > Cc: Lu Baolu <baolu...@linux.intel.com> > Suggested-by: Alex Williamson <alex.william...@redhat.com> > Signed-off-by: Liu Yi L <yi.l....@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]); >