Re: [PATCH v2 00/11] PCI: BAR resizing fix/rework

Bjorn Helgaas
2025-11-13T17:16:32Z

On Thu, Nov 13, 2025 at 06:26:17PM +0200, Ilpo Järvinen wrote:
> Hi all,
>
> Thanks to issue reports from Simon Richter and Alex Bennée, I
> discovered BAR resize rollback can corrupt the resource tree. As fixing
> corruption requires avoiding overlapping resource assignments, the
> correct fix can unfortunately results in worse user experience, what
> appeared to be "working" previously might no longer do so. Thus, I had
> to do a larger rework to pci_resize_resource() in order to properly
> restore resource states as it was prior to BAR resize.
>
> This rework has been on my TODO list anyway but it wasn't the highest
> prio item until pci_resize_resource() started to cause regressions due
> to other resource assignment algorithm changes.
>
> BAR resize rollback does not always restore BAR resources as they were
> before the resize operation was started. Currently, when
> pci_resize_resource() call is made by a driver, the driver must release
> device resource prior to the call. This is a design flaw in
> pci_resize_resource() API as PCI core cannot then save the state of
> those resources from what it was prior to release so it could restore
> them later if the BAR size change has to be rolled back.
>
> PCI core's BAR resize operation doesn't even attempt to restore the
> device resources currently when rolling back BAR resize operation. If
> the normal resource assignment algorithm assigned those resources, then
> device resources might be assigned after pci_resize_resource() call but
> that could also trigger the resource tree corruption issue so what
> appeared to an user as "working" might be a corrupted state.
>
> With the new pci_resize_resource() interface, the driver calling
> pci_resize_resource() should no longer release the device resources.
>
> I've added WARN_ON_ONCE() to pick up similar bugs that cause resource
> tree corruption. At least in my tests all looked clear on that front
> after this series.
>
> It would still be nice if the reporters could test these changes
> resolve the claim conflicts (while I've tested the series to some extent,
> I don't have such conflicts here).
>
> This series will likely conflict with some drm changes from Lucas (will
> make them partially obsolete by removing the need to release dev's
> resources on the driver side).
>
> I'll soon submit refresh of pci/rebar series on top of this series as
> there are some conflicts with them.
>
> v2:
> - Add exclude_bars parameter to pci_resize_resource()
> - Add Link tags
> - Add kerneldoc patch
> - Add patch to release pci_bus_sem earlier.
> - Fix to uninitialized var warnings.
> - Don't use guard() as goto from before it triggers error with clang.
>
> Ilpo Järvinen (11):
> PCI: Prevent resource tree corruption when BAR resize fails
> PCI/IOV: Adjust ->barsz[] when changing BAR size
> PCI: Change pci_dev variable from 'bridge' to 'dev'
> PCI: Try BAR resize even when no window was released
> PCI: Freeing saved list does not require holding pci_bus_sem
> PCI: Fix restoring BARs on BAR resize rollback path
> PCI: Add kerneldoc for pci_resize_resource()
> drm/xe: Remove driver side BAR release before resize
> drm/i915: Remove driver side BAR release before resize
> drm/amdgpu: Remove driver side BAR release before resize
> PCI: Prevent restoring assigned resources
>
> drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 10 +-
> drivers/gpu/drm/i915/gt/intel_region_lmem.c | 14 +--
> drivers/gpu/drm/xe/xe_vram.c | 5 +-
> drivers/pci/iov.c | 15 +--
> drivers/pci/pci-sysfs.c | 17 +--
> drivers/pci/pci.c | 4 +
> drivers/pci/pci.h | 9 +-
> drivers/pci/setup-bus.c | 126 ++++++++++++++------
> drivers/pci/setup-res.c | 52 ++++----
> include/linux/pci.h | 3 +-
> 10 files changed, 142 insertions(+), 113 deletions(-)

Applied to pci/resource for build testing.

Will watch for acks from xd, i915, amdgpu folks before merging.