ACK: [SRU X][PATCH 0/3] Add kernel parameter 'pci=clearmsi' to clear MSI(X)s early on boot

Stefan Bader 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)
> 
> [Impact]
> 
>  * 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]
> 
>    [1] [PATCH 1/3] x86/quirks: Scan all busses for early PCI quirks
>        https://lore.kernel.org/linux-pci/20181018183721.27467-1-gpiccoli@canonical.com/
> 
>    [2] [PATCH 2/3] x86/PCI: Export find_cap() to be used in early PCI code
>        https://lore.kernel.org/linux-pci/20181018183721.27467-2-gpiccoli@canonical.com/
> 
>    [3] [PATCH 3/3] x86/quirks: Add parameter to clear MSIs early on boot
>        https://lore.kernel.org/linux-pci/20181018183721.27467-3-gpiccoli@canonical.com/
> 
> 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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