On 9/6/19 7:00 PM, Igor Druzhinin wrote: > > On 06/09/2019 23:30, Boris Ostrovsky wrote: >> On 9/3/19 8:20 PM, Igor Druzhinin wrote: >>> If MCFG area is not reserved in E820, Xen by default will defer its usage >>> until Dom0 registers it explicitly after ACPI parser recognizes it as >>> a reserved resource in DSDT. Having it reserved in E820 is not >>> mandatory according to "PCI Firmware Specification, rev 3.2" (par. 4.1.2) >>> and firmware is free to keep a hole E820 in that place. Xen doesn't know >>> what exactly is inside this hole since it lacks full ACPI view of the >>> platform therefore it's potentially harmful to access MCFG region >>> without additional checks as some machines are known to provide >>> inconsistent information on the size of the region. >>> >>> Now xen_mcfg_late() runs after acpi_init() which is too late as some basic >>> PCI enumeration starts exactly there. Trying to register a device prior >>> to MCFG reservation causes multiple problems with PCIe extended >>> capability initializations in Xen (e.g. SR-IOV VF BAR sizing). There are >>> no convenient hooks for us to subscribe to so try to register MCFG >>> areas earlier upon the first invocation of xen_add_device(). >> >> Where is MCFG parsed? pci_arch_init()? > It happens twice: > 1) first time early one in pci_arch_init() that is arch_initcall - that > time pci_mmcfg_list will be freed immediately there because MCFG area is > not reserved in E820; > 2) second time late one in acpi_init() which is subsystem_initcall right > before where PCI enumeration starts - this time ACPI tables will be > checked for a reserved resource and pci_mmcfg_list will be finally > populated. > > The problem is that on a system that doesn't have MCFG area reserved in > E820 pci_mmcfg_list is empty before acpi_init() and our PCI hooks are > called in the same place. So MCFG is still not in use by Xen at this > point since we haven't reached our xen_mcfg_late().
Would it be possible for us to parse MCFG ourselves in pci_xen_init()? I realize that we'd be doing this twice (or maybe even three times since apparently both pci_arch_init() and acpi_ini() do it). -boris _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
