** Changed in: linux (Ubuntu Noble)
Importance: High => Medium
** Changed in: linux (Ubuntu Noble)
Status: In Progress => Fix Committed
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https://bugs.launchpad.net/bugs/2121146
Title:
[UBUNTU 24.04] vfio/pci: fix 8-byte PCI loads and stores
Status in Ubuntu on IBM z Systems:
In Progress
Status in linux package in Ubuntu:
Invalid
Status in linux source package in Noble:
Fix Committed
Bug description:
[ Impact ]
Reading from or writing to 64 bit registers (I/O ports or MMIO) on a
PCI adapter attached via vfio with e.g. the pread()/pwrite() system
calls may not work in case the PCI adapter requires a full read or
write that can not be broken up.
64 bit reads/writes are not implemented via the vfio I/O port or MMIO
access, even if the architecture supports 64 bit I/O reads and writes.
It is necessary to implement the use of 64 bit I/O reads and writes in
the vfio driver, so that such reads and writes are not broken up into
multiple smaller operations if the architecture supports such bigger
operations.
[ Fix ]
Backport the following commits in Noble:
- 186bfe44ea41 vfio/pci: Extract duplicated code into macro
- 4df13a6871d9 vfio/pci: Support 8-byte PCI loads and stores
- abe8103da3c5 vfio/pci: Fix typo in macro to declare accessors
[ Test Case ]
Bind a PCI device to vfio-pci and open it via /dev/vfio/<group>.
From user space, issue pread()/pwrite() calls with size 64-bit on the
device’s registers.
Use ftrace or similar tools to confirm
vfio_pci_core_ioread64/vfio_pci_core_iowrite64 is invoked.
If available, check that a device requiring atomic 64-bit access now works
correctly.
[ Regression Potential ]
The fix affects how VFIO PCI handles 64-bit register accesses via pread() and
pwrite() from user-space.
A bug here could cause incorrect or partial reads and writes to device
registers, breaking atomicity guarantees required by some PCI adapters.
Users may see devices misconfiguration, inconsistent register values,
unexpected hardware behavior, or even system instability when using user-space
drivers with VFIO.
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Description: vfio/pci: fix 8-byte PCI loads and stores
Symptom:
Reading from or writing to 64 bit registers (I/O ports or MMIO) on a PCI
adapter attached via vfio with e.g. the pread()/pwrite() system calls may not
work in case the PCI adapter requires a full read or write that can not be
broken up.
Problem:
64 bit reads/writes are not implemented via the vfio I/O port or MMIO access,
even if the architecture supports 64 bit I/O reads and writes.
Solution:
Implement the use of 64 bit I/O reads and writes in the vfio driver, so that
such reads and writes are not broken up into multiple smaller operations if the
architecture supports such bigger operations.
Upstream-IDs:
186bfe44ea41fb38c7a69becd7078724d28cd03c
4df13a6871d9e97aeeef72244e9a954c5cf11f54
Component: kernel
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