linux-kernel - A lingering doubt on PCI-MMIO region of PCI-passthrough-device

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Message-ID: <CAHP4M8Uy7HLiKjnMCdNG+QG+0cizN82c_G87AuzDL6qDCBG5vg@mail.gmail.com>
Date: Sun, 14 Dec 2025 17:38:50 +0530
From: Ajay Garg <ajaygargnsit@...il.com>
To: iommu@...ts.linux-foundation.org, linux-pci@...r.kernel.org, 
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: A lingering doubt on PCI-MMIO region of PCI-passthrough-device

Hi everyone.

Let's assume x86_64-linux host and guest, with full-virtualization and
iommu hardware capabilities.

Before launching vm, qemu with the help vfio "installs" "dev1" on the
virtual-pci-root-complex of guest.
After bootup, the guest does the usual enumeration, finds "dev1" on
the pci-bus, and programs the BARs in its domain.

However, there is no guarantee that guest-pci-mmio-physical-ranges
would be identical to "what would have been"
host-pci-mmio-physical-ranges.
Then how does the EPT/SLAT tables get set up for correct mapping from
GPA => HPA for dev1's-BARs-MMIO-regions ?

Will be grateful for pointers.

Thanks and Regards,
Ajay