Hi Bjorn,
On 12/30/21 4:42 AM, Bjorn Helgaas wrote:
On Fri, Dec 17, 2021 at 02:36:58PM +0800, Lu Baolu wrote:
The pci_dma_configure() marks the iommu_group as containing only devices
with kernel drivers that manage DMA.
I'm looking at pci_dma_configure(), and I don't see the connection to
iommu_groups.
The 2nd patch "driver core: Set DMA ownership during driver bind/unbind"
sets all drivers' DMA to be kernel-managed by default except a few ones
which has a driver flag set. So by default, all iommu groups contains
only devices with kernel drivers managing DMA.
Avoid this default behavior for the
pci_stub because it does not program any DMA itself. This allows the
pci_stub still able to be used by the admin to block driver binding after
applying the DMA ownership to vfio.
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
drivers/pci/pci-stub.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/pci/pci-stub.c b/drivers/pci/pci-stub.c
index e408099fea52..6324c68602b4 100644
--- a/drivers/pci/pci-stub.c
+++ b/drivers/pci/pci-stub.c
@@ -36,6 +36,9 @@ static struct pci_driver stub_driver = {
.name = "pci-stub",
.id_table = NULL, /* only dynamic id's */
.probe = pci_stub_probe,
+ .driver = {
+ .suppress_auto_claim_dma_owner = true,
The new .suppress_auto_claim_dma_owner controls whether we call
iommu_device_set_dma_owner(). I guess you added
.suppress_auto_claim_dma_owner because iommu_device_set_dma_owner()
must be done *before* we call the driver's .probe() method?
As explained above, all drivers are set to kernel-managed dma by
default. For those vfio and vfio-approved drivers,
suppress_auto_claim_dma_owner is used to tell the driver core that "this
driver is attached to device for userspace assignment purpose, do not
claim it for kernel-management dma".
Otherwise, we could call some new interface from .probe() instead of
adding the flag to struct device_driver.
Most device drivers are of the kernel-managed DMA type. Only a few vfio
and vfio-approved drivers need to use this flag. That's the reason why
we claim kernel-managed DMA by default.
+ },
};
static int __init pci_stub_init(void)
--
2.25.1
Best regards,
baolu
