On 2025-04-04 06:28, Roger Pau Monné wrote:
On Thu, Apr 03, 2025 at 06:01:42PM -0700, Stefano Stabellini wrote:
On one Sapphire AMD x86 board, I see this:
(XEN) [0000003943ca6ff2] [00000000f0000000, 00000000f7ffffff] (reserved)
(XEN) [00000039460886d9] [00000000fd000000, 00000000ffffffff] (reserved)
[...]
(XEN) [ 4.612235] 0000:02:00.0: not mapping BAR [fea00, fea03] invalid
position
Linux boots fine on this platform but Linux as Dom0 on Xen does not.
This is because the pci_check_bar->is_memory_hole check fails due to the
MMIO region overlapping with the EFI reserved region.
That's weird. (Partially) the reason to not attempt to map such BAR
is that it should already be mapped, because at dom0 creation time all
reserved regions are added to the p2m (see arch_iommu_hwdom_init()).
If that's not the case we should figure out why this reserved region
is not added to dom0 p2m as part of arch_iommu_hwdom_init().
Victor discovered these regions are type 11 EfiMemoryMappedIO, but they
get converted to e820 RESERVED. The BAR points into it.
00000f0000000-00000f7ffffff type=11 attr=800000000000100d
00000fd000000-00000fedfffff type=11 attr=800000000000100d
00000fee00000-00000fee00fff type=11 attr=8000000000000001
00000fee01000-00000ffffffff type=11 attr=800000000000100d
Xenia discovered Linux keeps small regions like this reserved, but lets
larger ones (>= 256kb) become holes. See the comment in Linux
arch/x86/platform/efi/efi.c:efi_remove_e820_mmio() around line 301.
The description of EfiMemoryMappedIO is a little confusing, which is
probably why its use in unclear.
```
Table 7.5 Memory Type Usage before ExitBootServices()
EfiMemoryMappedIO
Used by system firmware to request that a memory-mapped IO region be
mapped by the OS to a virtual address so it can be accessed by EFI
runtime services.
Table 7.6 Memory Type Usage after ExitBootServices()
EfiMemoryMappedIO
This memory is not used by the OS. All system memory-mapped IO
information should come from ACPI tables.
```
The two after ExitBootServices sentences seem contradictory. I wonder
if it should be "Ignore this memory type - All system memory-mapped IO
information should come from ACPI tables".
Can you paste the dom0 build output when booted with `iommu=verbose
dom0=pvh,verbose`? Does using `dom0=pvh,verbose,pf-fixup` solve the
boot issue? (and can you paste the output if it does)
pf-fixup did not resolve it. The vpci pci_check_bar() check is
independent of pf-fixup from what I can tell.
Regards,
Jason
