On Tue, 2 Feb 2021, Julien Grall wrote: > On 02/02/2021 18:12, Julien Grall wrote: > > On 02/02/2021 17:47, Elliott Mitchell wrote: > > > The handle_device() function has been returning failure upon > > > encountering a device address which was invalid.  A device tree which > > > had such an entry has now been seen in the wild.  As it causes no > > > failures to simply ignore the entries, ignore them. > > > > Signed-off-by: Elliott Mitchell > > > > > > --- > > > I'm starting to suspect there are an awful lot of places in the various > > > domain_build.c files which should simply ignore errors.  This is now the > > > second place I've encountered in 2 months where ignoring errors was the > > > correct action. > > > > Right, as a counterpoint, we run Xen on Arm HW for several years now and > > this is the first time I heard about issue parsing the DT. So while I > > appreciate that you are eager to run Xen on the RPI... > > > > >  I know failing in case of error is an engineer's > > > favorite approach, but there seem an awful lot of harmless failures > > > causing panics. > > > > > > This started as the thread "[RFC PATCH] xen/arm: domain_build: Ignore > > > empty memory bank".  Now it seems clear the correct approach is to simply > > > ignore these entries. > > > > ... we first need to fully understand the issues. Here a few questions: > >    1) Can you provide more information why you believe the address is > > invalid? > >    2) How does Linux use the node? > >    3) Is it happening with all the RPI DT? If not, what are the > > differences? > > So I had another look at the device-tree you provided earlier on. The node is > the following (copied directly from the DTS): > > &pcie0 { > pci@1,0 { > #address-cells = <3>; > #size-cells = <2>; > ranges; > > reg = <0 0 0 0 0>; > > usb@1,0 { > reg = <0x10000 0 0 0 0>; > resets = <&reset RASPBERRYPI_FIRMWARE_RESET_ID_USB>; > }; > }; > }; > > pcie0: pcie@7d500000 { > compatible = "brcm,bcm2711-pcie"; > reg = <0x0 0x7d500000 0x0 0x9310>; > device_type = "pci"; > #address-cells = <3>; > #interrupt-cells = <1>; > #size-cells = <2>; > interrupts = , > ; > interrupt-names = "pcie", "msi"; > interrupt-map-mask = <0x0 0x0 0x0 0x7>; > interrupt-map = <0 0 0 1 &gicv2 GIC_SPI 143 > IRQ_TYPE_LEVEL_HIGH>; > msi-controller; > msi-parent = <&pcie0>; > > ranges = <0x02000000 0x0 0xc0000000 0x6 0x00000000 > 0x0 0x40000000>; > /* > * The wrapper around the PCIe block has a bug > * preventing it from accessing beyond the first 3GB of > * memory. > */ > dma-ranges = <0x02000000 0x0 0x00000000 0x0 0x00000000 > 0x0 0xc0000000>; > brcm,enable-ssc; > }; > > The interpretation of "reg" depends on the context. In this case, we are > trying to interpret as a memory address from the CPU PoV when it has a > different meaning (I am not exactly sure what). > > In fact, you are lucky that Xen doesn't manage to interpret it. Xen should > really stop trying to look region to map when it discover a PCI bus. I wrote a > quick hack patch that should ignore it: Yes, I think you are right. There are a few instances where "reg" is not a address ready to be remapped. It is not just PCI, although that's the most common. Maybe we need a list, like skip_matches in handle_node. > diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c > index 374bf655ee34..937fd1e387b7 100644 > --- a/xen/arch/arm/domain_build.c > +++ b/xen/arch/arm/domain_build.c > @@ -1426,7 +1426,7 @@ static int __init handle_device(struct domain *d, struct > dt_device_node *dev, > > static int __init handle_node(struct domain *d, struct kernel_info *kinfo, > struct dt_device_node *node, > - p2m_type_t p2mt) > + p2m_type_t p2mt, bool pci_bus) > { > static const struct dt_device_match skip_matches[] __initconst = > { > @@ -1532,9 +1532,14 @@ static int __init handle_node(struct domain *d, struct > kernel_info *kinfo, > "WARNING: Path %s is reserved, skip the node as we may re-use > the path.\n", > path); > > - res = handle_device(d, node, p2mt); > - if ( res) > - return res; > + if ( !pci_bus ) > + { > + res = handle_device(d, node, p2mt); > + if ( res) > + return res; > + > + pci_bus = dt_device_type_is_equal(node, "pci"); > + } > > /* > * The property "name" is used to have a different name on older FDT > @@ -1554,7 +1559,7 @@ static int __init handle_node(struct domain *d, struct > kernel_info *kinfo, > > for ( child = node->child; child != NULL; child = child->sibling ) > { > - res = handle_node(d, kinfo, child, p2mt); > + res = handle_node(d, kinfo, child, p2mt, pci_bus); > if ( res ) > return res; > } > @@ -2192,7 +2197,7 @@ static int __init prepare_dtb_hwdom(struct domain *d, > struct kernel_info *kinfo) > > fdt_finish_reservemap(kinfo->fdt); > > - ret = handle_node(d, kinfo, dt_host, default_p2mt); > + ret = handle_node(d, kinfo, dt_host, default_p2mt, false); > if ( ret ) > goto err; > > A less hackish possibility would be to modify dt_number_of_address() and > return 0 when the device is a child of a PCI below. > > Stefano, do you have any opinions? Would PCIe even work today? Because if it doesn't, we could just add it to skip_matches until we get PCI passthrough properly supported. But aside from PCIe, let's say that we know of a few nodes for which "reg" needs a special treatment. I am not sure it makes sense to proceed with parsing those nodes without knowing how to deal with that. So maybe we should add those nodes to skip_matches until we know what to do with them. At that point, I would imagine we would introduce a special handle_device function that knows what to do. In the case of PCIe, something like "handle_device_pcie".