| Message ID | 20220228005056.599595-7-baolu.lu@linux.intel.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Fix BUG_ON in vfio_iommu_group_notifier() | expand |
On Mon, Feb 28, 2022 at 08:50:51AM +0800, Lu Baolu wrote: > If a switch lacks ACS P2P Request Redirect, a device below the switch can > bypass the IOMMU and DMA directly to other devices below the switch, so > all the downstream devices must be in the same IOMMU group as the switch > itself. > > The existing VFIO framework allows the portdrv driver to be bound to the > bridge while its downstream devices are assigned to user space. The > pci_dma_configure() marks the IOMMU group as containing only devices > with kernel drivers that manage DMA. Avoid this default behavior for the > portdrv driver in order for compatibility with the current VFIO usage. It would be nice to explicitly say here how we can look at portdrv (and pci_stub) and conclude that ".driver_managed_dma = true" is safe. Otherwise I won't know what kind of future change to portdrv might make it unsafe. > Suggested-by: Jason Gunthorpe <jgg@nvidia.com> > Suggested-by: Kevin Tian <kevin.tian@intel.com> > Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com> > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Bjorn Helgaas <bhelgaas@google.com> > --- > drivers/pci/pcie/portdrv_pci.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c > index 35eca6277a96..6b2adb678c21 100644 > --- a/drivers/pci/pcie/portdrv_pci.c > +++ b/drivers/pci/pcie/portdrv_pci.c > @@ -202,6 +202,8 @@ static struct pci_driver pcie_portdriver = { > > .err_handler = &pcie_portdrv_err_handler, > > + .driver_managed_dma = true, > + > .driver.pm = PCIE_PORTDRV_PM_OPS, > }; > > -- > 2.25.1 > > _______________________________________________ > iommu mailing list > iommu@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/iommu
Hi Bjorn, On 3/1/22 3:56 AM, Bjorn Helgaas wrote: > On Mon, Feb 28, 2022 at 08:50:51AM +0800, Lu Baolu wrote: >> If a switch lacks ACS P2P Request Redirect, a device below the switch can >> bypass the IOMMU and DMA directly to other devices below the switch, so >> all the downstream devices must be in the same IOMMU group as the switch >> itself. >> >> The existing VFIO framework allows the portdrv driver to be bound to the >> bridge while its downstream devices are assigned to user space. The >> pci_dma_configure() marks the IOMMU group as containing only devices >> with kernel drivers that manage DMA. Avoid this default behavior for the >> portdrv driver in order for compatibility with the current VFIO usage. > > It would be nice to explicitly say here how we can look at portdrv > (and pci_stub) and conclude that ".driver_managed_dma = true" is safe. > > Otherwise I won't know what kind of future change to portdrv might > make it unsafe. Fair enough. We can add below words: We achieve this by setting ".driver_managed_dma = true" in pci_driver structure. It is safe because the portdrv driver meets below criteria: - This driver doesn't use DMA, as you can't find any related calls like pci_set_master() or any kernel DMA API (dma_map_*() and etc.). - It doesn't use MMIO as you can't find ioremap() or similar calls. It's tolerant to userspace possibly also touching the same MMIO registers via P2P DMA access. > >> Suggested-by: Jason Gunthorpe <jgg@nvidia.com> >> Suggested-by: Kevin Tian <kevin.tian@intel.com> >> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com> >> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> > > Acked-by: Bjorn Helgaas <bhelgaas@google.com> Thank you! Best regards, baolu > >> --- >> drivers/pci/pcie/portdrv_pci.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c >> index 35eca6277a96..6b2adb678c21 100644 >> --- a/drivers/pci/pcie/portdrv_pci.c >> +++ b/drivers/pci/pcie/portdrv_pci.c >> @@ -202,6 +202,8 @@ static struct pci_driver pcie_portdriver = { >> >> .err_handler = &pcie_portdrv_err_handler, >> >> + .driver_managed_dma = true, >> + >> .driver.pm = PCIE_PORTDRV_PM_OPS, >> }; >> >> -- >> 2.25.1 >> >> _______________________________________________ >> iommu mailing list >> iommu@lists.linux-foundation.org >> https://lists.linuxfoundation.org/mailman/listinfo/iommu
diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c index 35eca6277a96..6b2adb678c21 100644 --- a/drivers/pci/pcie/portdrv_pci.c +++ b/drivers/pci/pcie/portdrv_pci.c @@ -202,6 +202,8 @@ static struct pci_driver pcie_portdriver = { .err_handler = &pcie_portdrv_err_handler, + .driver_managed_dma = true, + .driver.pm = PCIE_PORTDRV_PM_OPS, };