On Mon, Feb 29, 2016 at 04:44:17PM -0600, Bjorn Helgaas wrote: > On Thu, Feb 25, 2016 at 03:41:51PM +0000, Lawrynowicz, Jacek wrote: > > > -----Original Message----- > > > From: Bjorn Helgaas [mailto:helgaas@xxxxxxxxxx] > > > Sent: Thursday, February 25, 2016 3:39 PM > > > To: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > > > Cc: Lawrynowicz, Jacek <jacek.lawrynowicz@xxxxxxxxx>; linux- > > > pci@xxxxxxxxxxxxxxx; Alex Williamson <alex.williamson@xxxxxxxxxx>; Joerg > > > Roedel <jroedel@xxxxxxx>; David Woodhouse <dwmw2@xxxxxxxxxxxxx>; > > > iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx > > > Subject: Re: [PATCH v4 3/6] PCI: Add support for multiple DMA aliases > > > > > > On Wed, Feb 24, 2016 at 01:44:06PM -0600, Bjorn Helgaas wrote: > > > > From: Jacek Lawrynowicz <jacek.lawrynowicz@xxxxxxxxx> > > What about my questions on the code itself, below? > Sorry but I'm not able to answer it. Maybe Joerg or David could help here? > > > > --- > > > > drivers/iommu/iommu.c | 17 ++++++++++------- > > > > drivers/pci/pci.c | 11 +++++++++-- > > > > drivers/pci/probe.c | 1 + > > > > drivers/pci/search.c | 14 +++++++++----- > > > > include/linux/pci.h | 4 +--- > > > > 5 files changed, 30 insertions(+), 17 deletions(-) > > > > > > > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > > > > index 0e3b009..a214e19 100644 > > > > --- a/drivers/iommu/iommu.c > > > > +++ b/drivers/iommu/iommu.c > > > > @@ -659,9 +659,15 @@ static struct iommu_group > > > *get_pci_function_alias_group(struct pci_dev *pdev, > > > > return NULL; > > > > } > > > > > > > > +static bool dma_alias_is_enabled(struct pci_dev *dev, u8 devfn) > > > > +{ > > > > + return dev->dma_alias_mask && > > > > + test_bit(devfn, dev->dma_alias_mask); > > > > +} > > > > + > > > > /* > > > > - * Look for aliases to or from the given device for exisiting groups. The > > > > - * dma_alias_devfn only supports aliases on the same bus, therefore the > > > search > > > > + * Look for aliases to or from the given device for existing groups. DMA > > > > + * aliases are only supported on the same bus, therefore the search > > > > > > I'm trying to reconcile this statement that "DMA aliases are only > > > supported on the same bus" (which was there even before this patch) > > > with the fact that pci_for_each_dma_alias() does not have that > > > limitation. > > > > > > > * space is quite small (especially since we're really only looking at pcie > > > > * device, and therefore only expect multiple slots on the root complex or > > > > * downstream switch ports). It's conceivable though that a pair of > > > > @@ -686,11 +692,8 @@ static struct iommu_group *get_pci_alias_group(struct > > > pci_dev *pdev, > > > > continue; > > > > > > > > /* We alias them or they alias us */ > > > > - if (((pdev->dev_flags & PCI_DEV_FLAGS_DMA_ALIAS_DEVFN) > > > && > > > > - pdev->dma_alias_devfn == tmp->devfn) || > > > > - ((tmp->dev_flags & PCI_DEV_FLAGS_DMA_ALIAS_DEVFN) && > > > > - tmp->dma_alias_devfn == pdev->devfn)) { > > > > - > > > > + if (dma_alias_is_enabled(pdev, tmp->devfn) || > > > > + dma_alias_is_enabled(tmp, pdev->devfn)) { > > > > group = get_pci_alias_group(tmp, devfns); > > > > > > We basically have this: > > > > > > for_each_pci_dev(tmp) { > > > if (<pdev and tmp are DMA aliases>) > > > group = get_pci_alias_group(); > > > ... > > > } > > > > > > The DMA alias stuff relies on PCI internals, so it doesn't doesn't > > > seem quite right to use things like PCI_DEV_FLAGS_DMA_ALIAS_DEVFN and > > > dma_alias_devfn here in the IOMMU code. > > > > > > I'm trying to figure out why we don't do something like the following > > > instead: > > > > > > callback(struct pci_dev *pdev, u16 alias, void *opaque) > > > { > > > struct iommu_group *group; > > > > > > group = get_pci_alias_group(); > > > if (group) > > > return group; > > > > > > return 0; > > > } > > > > > > pci_for_each_dma_alias(pdev, callback, ...); > > > > > > Is the existing code some sort of optimization, e.g., checking > > > PCI_DEV_FLAGS_DMA_ALIAS_DEVFN is cheaper than using > > > pci_for_each_dma_alias()? > > > > > > It seems like this won't work for some very unlikely but theoretically > > > possible topologies, e.g., > > > > > > PCIe Root Complex/IOMMU > > > PCIe switch A > > > PCIe to conventional PCI bridge > > > PCI to PCIe Root Complex > > > PCIe NTB > > > > > > Here, I think the IOMMU will only see RIDs from PCIe switch A, but the > > > current code only looks at DMA aliases that are on the same bus as the > > > PCIe NTB. Wouldn't using pci_for_each_dma_alias() handle this > > > correctly? > > > > > > > if (group) { > > > > pci_dev_put(tmp); > > -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
