On 12/31/21 6:24 AM, Bjorn Helgaas wrote:
On Thu, Dec 30, 2021 at 01:34:27PM +0800, Lu Baolu wrote:
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.
It looks like that happens in device_dma_configure(), not
pci_dma_configure().
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.
Yes. But you didn't answer the question of whether this must be done
by a new flag in struct device_driver, or whether it could be done by
having these few VFIO and "VFIO-approved" (whatever that means)
drivers call a new interface.
I was speculating that maybe the DMA ownership claiming must be done
*before* the driver's .probe() method? If so, that would require a
new flag. But I don't know whether that's the case. If DMA
ownership could be claimed by the .probe() method, we wouldn't need
the new flag in struct device_driver.
Yes. It's feasible. Hence we can remove the suppress flag which is only
for some special drivers. I will come up with a new version so that you
can further comment with the real code. Thank you!
Bjorn
Best regards,
baolu
