[U][PATCH v2 0/3] Add kernel parameter 'pci=clearmsi' to clear MSI(X)s early on boot
Mauricio Faria de Oliveira
mfo at canonical.com
Thu Nov 8 21:07:18 UTC 2018
- Reorder patch 1 as 3 to allow for the next change:
- Gate the bus-scan differences with the cmdline option
(patch 3 only). Now all functional changes are gated.
* A kexec/crash kernel might get stuck and fail to boot
(for crash kernel, kdump fails to collect a crashdump)
if a PCI device is buggy/stuck/looping and triggers a
continuous flood of MSI(X) interrupts (that the kernel
does not yet know about).
* This fix allowed to obtain crashdumps when debugging a
heavy-load scenario, in which a (heavy-loaded) network
adapter wouldn't stop triggering MSI-X interrupts ever
after panic()->kdump kicked in.
* This fix disables MSI(X) in all PCI devices on early
boot (this is OK as it's (re-)enabled normally later)
with a kernel cmdline parameter (disabled by default).
* A synthetic test-case is not yet available, however,
this particular system/workload triggered the problem
consistently, and it was used for development/testing.
* We'll update this bug once a synthetic test-case is
available; we're working on patching QEMU for this.
* $ dmesg | grep 'Clearing MSI'
[ 0.000000] Clearing MSI/MSI-X enable bits early in boot (quirk)
* The comparison of 'dmesg -t | sort' has been reviewed
between option disabled/enabled on boot & kexec modes,
and only expected differences found (MHz, PIDs, MIPS).
* The potential area for regressions is early boot,
particularly effects of applying quirks during PCI
bus scan, which is changed/broader w/ these patches.
* However, all quirks are applied based on PCI ID
matching, so would only apply if actually targeting
a new device.
* Moreover, the new quirk is only applied based on
a kernel cmdline parameter that is disabled by
default, which constraints even more when this
is actually in effect.
* The patch series is still under review/discussion
upstream, but it's relatively important for Ubuntu
users at this point, and after internal discussions
we decided to submit it for SRU.
* These are links to the linux-pci archive with the
patches [1, 2, 3]
 [PATCH 1/3] x86/quirks: Scan all busses for early PCI quirks
 [PATCH 2/3] x86/PCI: Export find_cap() to be used in early PCI code
 [PATCH 3/3] x86/quirks: Add parameter to clear MSIs early on boot
Guilherme G. Piccoli (3):
UBUNTU: SAUCE: x86/PCI: Export find_cap() to be used in early PCI code
UBUNTU: SAUCE: x86/quirks: Add parameter to clear MSIs early on boot
UBUNTU: SAUCE: x86/quirks: Scan all busses for early PCI quirks
.../admin-guide/kernel-parameters.txt | 6 +++
arch/x86/include/asm/pci-direct.h | 2 +
arch/x86/kernel/aperture_64.c | 30 +-------------
arch/x86/kernel/early-quirks.c | 41 +++++++++++++++++++
arch/x86/pci/common.c | 4 ++
arch/x86/pci/early.c | 25 +++++++++++
6 files changed, 80 insertions(+), 28 deletions(-)
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