From: "Guilherme G. Piccoli" <gpiccoli@canonical.com>
To: Bjorn Helgaas <helgaas@kernel.org>, tglx@linutronix.de
Cc: linux-pci@vger.kernel.org, kexec@lists.infradead.org,
x86@kernel.org, linux-kernel@vger.kernel.org,
bhelgaas@google.com, dyoung@redhat.com, bhe@redhat.com,
vgoyal@redhat.com, mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
andi@firstfloor.org, lukas@wunner.de, okaya@kernel.org,
kernelfans@gmail.com, ddstreet@canonical.com,
gavin.guo@canonical.com, jay.vosburgh@canonical.com,
kernel@gpiccoli.net, shan.gavin@linux.alibaba.com
Subject: Re: [PATCH 1/3] x86/quirks: Scan all busses for early PCI quirks
Date: Fri, 6 Nov 2020 10:14:14 -0300 [thread overview]
Message-ID: <684cf38f-3977-4ec2-c4a6-7c4c31f9851a@canonical.com> (raw)
In-Reply-To: <20181023170343.GA4587@bhelgaas-glaptop.roam.corp.google.com>
On 23/10/2018 14:03, Bjorn Helgaas wrote:
> On Mon, Oct 22, 2018 at 05:35:06PM -0300, Guilherme G. Piccoli wrote:
>> On 18/10/2018 19:15, Bjorn Helgaas wrote:
>>> On Thu, Oct 18, 2018 at 03:37:19PM -0300, Guilherme G. Piccoli wrote:
>>> [...]
>> I understand your point, but I think this is inherently an architecture
>> problem. No matter what solution we decide for, it'll need to be applied
>> in early boot time, like before the PCI layer gets initialized.
>
> This is the part I want to know more about. Apparently there's some
> event X between early_quirks() and the PCI device enumeration, and we
> must disable MSIs before X:
>
> setup_arch()
> early_quirks() # arch/x86/kernel/early-quirks.c
> early_pci_clear_msi()
> ...
> X
> ...
> pci_scan_root_bus_bridge()
> ...
> DECLARE_PCI_FIXUP_EARLY # drivers/pci/quirks.c
>
> I want to know specifically what X is. If we don't know what X is and
> all we know is "we have to disable MSIs earlier than PCI init", then
> we're likely to break things again in the future by changing the order
> of disabling MSIs and whatever X is.
>
> Bjorn
>
Hi Bjorn (and all CCed), I'm sorry to necro-bump a thread >2 years
later, but recent discussions led to a better understanding of this 'X'
point, thanks to Thomas!
For those that deleted this thread from their email clients, it's
available in [0] - the summary is that we faced an IRQ storm really
early in boot, due to a bogus PCIe device MSI behavior, when booting a
kdump kernel. This led the machine to get stuck in the boot and we
couldn't kdump. The solution hereby proposed is to clear MSI interrupts
early in x86, if a parameter is provided. I don't have the reproducer
anymore and it was pretty hard to reproduce in virtual environments.
So, about the 'X' Bjorn, in another recent thread about IRQ storms [1],
Thomas clarified that and after a brief discussion, it seems there's no
better way to prevent the MSI storm other than clearing the MSI
capability early in boot. As discussed both here and in thread [1], this
is indeed a per-architecture issue (powerpc is not subject to that, due
to a better FW reset mechanism), so I think we still could benefit in
having this idea implemented upstream, at least in x86 (we could expand
to other architectures if desired, in the future).
As a "test" data point, this was implemented in Ubuntu (same 3 patches
present in this series) for ~2 years and we haven't received bug reports
- I'm saying that because I understand your concerns about expanding the
early PCI quirks scope.
Let me know your thoughts. I'd suggest all to read thread [1], which
addresses a similar issue but in a different "moment" of the system boot
and provides some more insight on why the early MSI clearing seems to
make sense.
Thanks,
Guilherme
[0]
https://lore.kernel.org/linux-pci/20181018183721.27467-1-gpiccoli@canonical.com
[1] https://lore.kernel.org/lkml/87y2js3ghv.fsf@nanos.tec.linutronix.de
next prev parent reply other threads:[~2020-11-06 13:14 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-18 18:37 [PATCH 1/3] x86/quirks: Scan all busses for early PCI quirks Guilherme G. Piccoli
2018-10-18 18:37 ` [PATCH 2/3] x86/PCI: Export find_cap() to be used in early PCI code Guilherme G. Piccoli
2018-10-18 18:37 ` [PATCH 3/3] x86/quirks: Add parameter to clear MSIs early on boot Guilherme G. Piccoli
2018-10-18 20:08 ` Sinan Kaya
2018-10-18 20:13 ` Guilherme G. Piccoli
2018-10-18 20:30 ` Sinan Kaya
2018-10-22 19:44 ` Guilherme G. Piccoli
2018-10-18 22:15 ` [PATCH 1/3] x86/quirks: Scan all busses for early PCI quirks Bjorn Helgaas
2018-10-22 20:35 ` Guilherme G. Piccoli
2018-10-23 17:03 ` Bjorn Helgaas
2020-11-06 13:14 ` Guilherme G. Piccoli [this message]
2020-11-13 16:46 ` Bjorn Helgaas
2020-11-13 23:31 ` Thomas Gleixner
2020-11-13 23:40 ` Thomas Gleixner
2020-11-14 20:39 ` Bjorn Helgaas
2020-11-14 20:58 ` Thomas Gleixner
2020-11-14 21:22 ` Bjorn Helgaas
2020-11-15 14:05 ` Eric W. Biederman
2020-11-15 14:29 ` Eric W. Biederman
2020-11-15 15:11 ` Thomas Gleixner
2020-11-15 17:01 ` Lukas Wunner
2020-11-15 19:18 ` Thomas Gleixner
2020-11-15 20:46 ` Eric W. Biederman
2020-11-16 20:31 ` Guilherme G. Piccoli
2020-11-16 21:45 ` Eric W. Biederman
2020-11-16 21:49 ` Guilherme Piccoli
2020-11-17 0:19 ` Bjorn Helgaas
2020-11-17 1:06 ` Eric W. Biederman
2020-11-17 9:53 ` Thomas Gleixner
2020-11-17 12:19 ` David Woodhouse
2020-11-17 19:34 ` Thomas Gleixner
2020-11-17 22:25 ` Eric W. Biederman
2020-11-17 12:04 ` Guilherme Piccoli
2020-11-18 21:05 ` Bjorn Helgaas
2020-11-18 22:36 ` Guilherme Piccoli
2020-11-30 20:20 ` Bjorn Helgaas
2020-12-14 18:32 ` Guilherme Piccoli
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