Messages in this thread | | | Subject | Re: [PATCH v4 03/13] PCI: pci_stub: Suppress kernel DMA ownership auto-claiming | From | Lu Baolu <> | Date | Thu, 30 Dec 2021 13:34:27 +0800 |
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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@linux.intel.com> >> --- >> 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
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