[Bug 287492] Unable to detect NIC cards on few PCIe Gen5 slots on Dell R770 servers where x2APIC mode is enabled

From: <bugzilla-noreply_at_freebsd.org>
Date: Sat, 21 Jun 2025 19:48:56 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=287492

John Baldwin <jhb@FreeBSD.org> changed:

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                 CC|                            |kib@FreeBSD.org

--- Comment #3 from John Baldwin <jhb@FreeBSD.org> ---
The issue is that for this system we need to support it's I/O MMU that is used
to remap APIC IDs used in I/O APIC and MSI interrupts so that the interrupt
message uses an APIC ID < 255, but it after it is remapped by the I/O MMU it
ends up using a "real" APIC ID that can be larger.

There are separate I/O MMU drivers for Intel systems (DMAR) vs AMD.  14.2
should have support for DMAR, but I believe only 15.0 has support for AMD's I/O
MMU (and I'm not fully certain if interrupt remapping is enabled by default for
AMD in 15.0).  Can you confirm which CPU vendor you are using?

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