Messages in this thread | | | Date | Thu, 17 Mar 2022 17:15:22 +0000 | Subject | Re: [PATCH 4/4 RESEND] PCI: hv: Propagate coherence from VMbus device to PCI device | From | Robin Murphy <> |
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On 2022-03-17 16:25, Michael Kelley via iommu wrote: > PCI pass-thru devices in a Hyper-V VM are represented as a VMBus > device and as a PCI device. The coherence of the VMbus device is > set based on the VMbus node in ACPI, but the PCI device has no > ACPI node and defaults to not hardware coherent. This results > in extra software coherence management overhead on ARM64 when > devices are hardware coherent. > > Fix this by propagating the coherence of the VMbus device to the > PCI device. There's no effect on x86/x64 where devices are > always hardware coherent. > > Signed-off-by: Michael Kelley <mikelley@microsoft.com> > --- > drivers/pci/controller/pci-hyperv.c | 17 +++++++++++++---- > 1 file changed, 13 insertions(+), 4 deletions(-) > > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c > index ae0bc2f..14276f5 100644 > --- a/drivers/pci/controller/pci-hyperv.c > +++ b/drivers/pci/controller/pci-hyperv.c > @@ -49,6 +49,7 @@ > #include <linux/refcount.h> > #include <linux/irqdomain.h> > #include <linux/acpi.h> > +#include <linux/dma-map-ops.h> > #include <asm/mshyperv.h> > > /* > @@ -2142,9 +2143,9 @@ static void hv_pci_remove_slots(struct hv_pcibus_device *hbus) > } > > /* > - * Set NUMA node for the devices on the bus > + * Set NUMA node and DMA coherence for the devices on the bus > */ > -static void hv_pci_assign_numa_node(struct hv_pcibus_device *hbus) > +static void hv_pci_assign_properties(struct hv_pcibus_device *hbus) > { > struct pci_dev *dev; > struct pci_bus *bus = hbus->bridge->bus; > @@ -2167,6 +2168,14 @@ static void hv_pci_assign_numa_node(struct hv_pcibus_device *hbus) > numa_map_to_online_node( > hv_dev->desc.virtual_numa_node)); > > + /* > + * On ARM64, propagate the DMA coherence from the VMbus device > + * to the corresponding PCI device. On x86/x64, these calls > + * have no effect because DMA is always hardware coherent. > + */ > + dev_set_dma_coherent(&dev->dev, > + dev_is_dma_coherent(&hbus->hdev->device));
Eww... if you really have to do this, I'd prefer to see a proper hv_dma_configure() helper implemented and wired up to pci_dma_configure(). Although since it's a generic property I guess at worst pci_dma_configure could perhaps propagate coherency from the host bridge to its children by itself in the absence of any other firmware info. And it's built-in so could use arch_setup_dma_ops() like everyone else.
Robin.
> + > put_pcichild(hv_dev); > } > } > @@ -2191,7 +2200,7 @@ static int create_root_hv_pci_bus(struct hv_pcibus_device *hbus) > return error; > > pci_lock_rescan_remove(); > - hv_pci_assign_numa_node(hbus); > + hv_pci_assign_properties(hbus); > pci_bus_assign_resources(bridge->bus); > hv_pci_assign_slots(hbus); > pci_bus_add_devices(bridge->bus); > @@ -2458,7 +2467,7 @@ static void pci_devices_present_work(struct work_struct *work) > */ > pci_lock_rescan_remove(); > pci_scan_child_bus(hbus->bridge->bus); > - hv_pci_assign_numa_node(hbus); > + hv_pci_assign_properties(hbus); > hv_pci_assign_slots(hbus); > pci_unlock_rescan_remove(); > break;
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