[Bug 220057] Kernel regression. Linux VMs crashing (I did not test Windows guest VMs)

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=220057

--- Comment #46 from Alex Williamson (alex.williamson@redhat.com) ---
Thanks for the prompt testing, I've posted the fix without the debug logging
here:

https://lore.kernel.org/all/20250502224035.3183451-1-alex.williamson@redhat.com/

Pending reviews and comments, I'll try to get it in for v6.15 for backport to
stable trees.

The VFIO_MAP_DMA failures are a VM configuration error and a byproduct that
Intel ships platforms where the CPU physical address width is different from
the IOMMU address width.  QEMU/vBIOS defines the MMIO layout relative to the
CPU address width, therefore the vCPU needs to reflect that address width
restriction.  QEMU makes this configuration available though a guest_phys_bits
option, but it doesn't appear that Proxmox provides a way to configure this. 
The result is these error logs, which indicate P2P DMA mappings are not being
created.  With the fix we're pursuing above, this should not result in a
performance/efficiency loss relative to the page table use though.

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