Re: [PATCH] x86/resource: Do not exclude regions that are marked as MMIO in EFI memmap

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Mon, Mar 02, 2020 at 05:14:51PM +0300, Mika Westerberg wrote:
> Commit 4dc2287c1805 ("x86: avoid E820 regions when allocating address
> space") made the resource allocation code to avoid all regions that are
> in E820 table. This prevents the kernel to assign MMIO resources to
> regions that may be real RAM for example.
> 
> However, at least with Lenovo Yoca C940 and S740 this causes problems
> when allocating resources for PCIe devices behind Thunderbolt port(s).
> 
> On Yoga S740 the E820 table contains an entry like this:
> 
>   BIOS-e820: [mem 0x000000002bc50000-0x00000000cfffffff] reserved
> 
> and ACPI _CRS method for the host bridge returns these windows:
> 
>   pci_bus 0000:00: root bus resource [io  0x0000-0x0cf7 window]
>   pci_bus 0000:00: root bus resource [io  0x0d00-0xffff window]
>   pci_bus 0000:00: root bus resource [mem 0x000a0000-0x000bffff window]
>   pci_bus 0000:00: root bus resource [mem 0x45400000-0xbfffffff window]
>   pci_bus 0000:00: root bus resource [mem 0x4000000000-0x7fffffffff window]
> 
> Note that the 0x45400000-0xbfffffff entry is also included in the E820
> table and marked as "reserved".
> 
> When Thunderbolt device is connected and the PCIe gets tunneled PCI core
> tries to allocate memory for the new devices but it fails because all
> the resources are inside this reserved region so arch_remove_reservations()
> clips them which makes the resource assignment fail as in below log:
> 
>   pci 0000:00:07.0: PCI bridge to [bus 01-2a]
>   pci 0000:00:07.0:   bridge window [mem 0x46000000-0x521fffff]
>   pci 0000:00:07.0:   bridge window [mem 0x6000000000-0x601bffffff 64bit pref]
>   ...
>   pci 0000:02:04.0: bridge window [mem 0x00100000-0x001fffff 64bit pref] to [bus 07-2a] add_size 100000 add_align 100000
>   pci 0000:02:04.0: bridge window [mem 0x00100000-0x001fffff] to [bus 07-2a] add_size 100000 add_align 100000
>   pci 0000:01:00.0: bridge window [mem 0x00100000-0x005fffff 64bit pref] to [bus 02-2a] add_size 100000 add_align 100000
>   pci 0000:01:00.0: bridge window [mem 0x00100000-0x005fffff] to [bus 02-2a] add_size 100000 add_align 100000
>   pci 0000:01:00.0: bridge window [io  0x1000-0x5fff] shrunken by 0x0000000000004000
>   pci 0000:01:00.0: bridge window [mem 0x00100000-0x005fffff] extended by 0x000000000bd00000
>   pci 0000:01:00.0: bridge window [mem 0x00100000-0x005fffff 64bit pref] extended by 0x000000001bb00000
>   pci 0000:02:04.0: bridge window [mem 0x00100000-0x001fffff] extended by 0x000000000bd00000
>   pci 0000:02:04.0: bridge window [mem 0x00100000-0x001fffff 64bit pref] extended by 0x000000001bb00000
>   pci 0000:01:00.0: BAR 8: no space for [mem size 0x0c200000]
>   pci 0000:01:00.0: BAR 8: failed to assign [mem size 0x0c200000]
>   pci 0000:01:00.0: BAR 9: assigned [mem 0x6000000000-0x601bffffff 64bit pref]
>   pci 0000:01:00.0: BAR 7: assigned [io  0x4000-0x4fff]
> 
> The 01:00.0 is the upstream port of the PCIe switch that is connected to
> the PCIe root port (00:07.1) over Thunderbolt link.
> 
> If I add "efi=debug" to the command line I can see that the EFI memory
> map actually contains several entries:
> 
>   [Reserved           |   |  |  |  |  |  |  | |   |WB|WT|WC|UC] range=[0x000000002bc50000-0x000000003fffffff] (323MB)
>   [Reserved           |   |  |  |  |  |  |  | |   |WB|  |  |UC] range=[0x0000000040000000-0x0000000040ffffff] (16MB)
>   [Reserved           |   |  |  |  |  |  |  | |   |  |  |  |  ] range=[0x0000000041000000-0x00000000453fffff] (68MB)
>   [Memory Mapped I/O  |RUN|  |  |  |  |  |  | |   |  |  |  |UC] range=[0x0000000045400000-0x00000000cfffffff] (2220MB)
> 
> I think the EFI stub merges these consecutive entries into that single
> E820 entry showed above. The last region marked as EFI_MEMORY_MAPPED_IO
> actually covers the PCI host bridge window entirely. However, since
> there is corresponding E820 type for this it is simply marked as
> E820_TYPE_RESERVED.
> 
> All in all, I think we can fix this by modifying arch_remove_reservations()
> to check the EFI type as well and if it is EFI_MEMORY_MAPPED_IO skip the
> clipping in that case.
> 
> Reported-by: Benoit Grégoire <benoitg@coeus.ca>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206459
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

Hello, any comments for this?