ACK: [SRU X][PATCH 0/3] Add kernel parameter 'pci=clearmsi' to clear MSI(X)s early on boot
stefan.bader at canonical.com
Thu Nov 8 09:51:00 UTC 2018
On 08.11.18 02:12, Mauricio Faria de Oliveira wrote:
> BugLink: https://bugs.launchpad.net/bugs/1797990
> (note: the patch set for later releases will be sent soon)
> * 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).
> [Test Case]
> * 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).
> [Regression Potential]
> * 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.
> [Other Info]
> * 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/quirks: Scan all busses for early PCI quirks
> 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
> Documentation/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 | 45 ++++++++++++++++++++++++-----
> arch/x86/pci/common.c | 4 +++
> arch/x86/pci/early.c | 25 ++++++++++++++++
> 6 files changed, 77 insertions(+), 35 deletions(-)
Since at least the new code is off by default the risk should be acceptable.
Acked-by: Stefan Bader <stefan.bader at canonical.com>
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