tree c0e3566598326faf26537533165008b2368cda9d
parent ecee523e53c8d8770b16a185fd78eaa26c48a3bc
author Rayan Dasoriya <dasoriya@google.com> 1644869211 +0000
committer Rayan Dasoriya <dasoriya@google.com> 1650666301 +0000

x86/quirks: Scan all busses for early PCI quirks

Recently was noticed in an HP GEN9 system that kdump couldn't succeed
due to an irq storm coming from an Intel NIC, narrowed down to be lack
of clearing the MSI/MSI-X enable bits during the kdump kernel boot.
For that, we need an early quirk to manually turn off MSI/MSI-X for
PCI devices - this was worked as an optional boot parameter in a
subsequent patch.

Problem is that in our test system, the Intel NICs were not present in
any secondary bus under the first PCIe root complex, so they couldn't
be reached by the recursion in check_dev_quirk(). Modern systems,
specially with multi-processors and multiple NUMA nodes expose multiple
root complexes, describing more than one PCI hierarchy domain. Currently
the simple recursion present in the early-quirks code from x86 starts a
descending recursion from bus 0000:00, and reach many other busses by
navigating this hierarchy walking through the bridges. This is not
enough in systems with more than one root complex/host bridge, since
the recursion won't "traverse" to other root complexes by starting
statically in 0000:00 (for more details, see [0]).

This patch hence implements the full bus/device/function scan in
early_quirks(), by checking all possible busses instead of using a
recursion based on the first root bus or limiting the search scope to
the first 32 busses (like it was done in the beginning [1]).

[0] https://bugs.launchpad.net/bugs/1797990

[1] From historical perspective, early PCI scan dates back
to BitKeeper, added by Andi Kleen's "[PATCH] APIC fixes for x86-64",
on October/2003. It initially restricted the search to the first
32 busses and slots.

Due to a potential bug found in Nvidia chipsets, the scan
was changed to run only in the first root bus: see
commit 8659c406ade3 ("x86: only scan the root bus in early PCI quirks")

Finally, secondary busses reachable from the 1st bus were re-added back by:
commit 850c321027c2 ("x86/quirks: Reintroduce scanning of secondary buses")

Reported-by: Dan Streetman <ddstreet@canonical.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@canonical.com>

BUG=b/160734277
TEST=presubmit and validation
RELEASE_NOTE=x86/quirks: Scan all busses for early PCI quirks
SOURCE=FROMLIST(https://lore.kernel.org/linux-pci/20181018183721.27467-1-gpiccoli@canonical.com/)

cos-patch: lts-refresh
Signed-off-by: Guilherme G. Piccoli <gpiccoli@canonical.com>
Change-Id: Ie6204b709a1760331bc5fa069a2a4b12f4655566
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/29401
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Oleksandr Tymoshenko <ovt@google.com>
(cherry picked from commit 62fd7552f50d41fd5eee1dc6882ab3c114b39b43)
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/32042
Main-Branch-Verified: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>