[U][PATCH v2 0/3] Add kernel parameter 'pci=clearmsi' to clear MSI(X)s early on boot

[Mauricio Faria de Oliveira]

Oops -- that should be Unstable, as requested by Cascardo. I realized later
than U could also refer to the old Utopic.
Sorry for the confusion.

On Mon, Nov 12, 2018 at 3:07 AM Khaled Elmously <
khalid.elmously at canonical.com> wrote:

> I'm not sure what is meant by [U] in the subject - what release is this
> intended for?
>
>
> On 2018-11-08 19:07:18 , Mauricio Faria de Oliveira wrote:
> > BugLink: https://bugs.launchpad.net/bugs/1797990
> >
> > [Changelog]
> >  * v2:
> >    - 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.
> >
> > [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/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(-)
> >
> > --
> > 2.17.1
> >
> >
> > --
> > kernel-team mailing list
> > kernel-team at lists.ubuntu.com
> > https://lists.ubuntu.com/mailman/listinfo/kernel-team
>


-- 
Mauricio Faria de Oliveira
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