Messages in this thread | | | Subject | Re: [PATCH] xen/pci: try to reserve MCFG areas earlier | From | Boris Ostrovsky <> | Date | Sun, 8 Sep 2019 19:30:41 -0400 |
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On 9/8/19 5:11 PM, Igor Druzhinin wrote: > On 08/09/2019 19:28, Boris Ostrovsky wrote: >> On 9/6/19 7:00 PM, Igor Druzhinin wrote: >>> On 06/09/2019 23:30, Boris Ostrovsky wrote: >>>> 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). >> > I don't thine it makes sense: > a) it needs to be done after ACPI is initialized since we need to parse > it to figure out the exact reserved region - that's why it's currently > done in acpi_init() (see commit message for the reasons why)
Hmm... We should be able to parse ACPI tables by the time pci_arch_init() is called. In fact, if you look at pci_mmcfg_early_init() you will see that it does just that.
> b) given (a) we cannot do it ourselves before acpi_init and after is too > late as we're already past ACPI PCI enumeration > c) we'd have to do it in the same place I call xen_mcfg_late() and it'd > be code duplication of what's already done by the existing code.
If we manage to parse MCFG ourselves early then maybe we won't not need xen_mcfg_late()? We can call PHYSDEVOP_pci_mmcfg_reserved right away.
-boris
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