linux-kernel - Re: [RFC PATCH] PCI, kdump: Clear bus master bit upon shutdown in kdump kernel

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Date:   Tue, 3 Mar 2020 13:01:04 -0800
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     Kairui Song <kasong@...hat.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Khalid Aziz <khalid@...ehiking.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org, kexec@...ts.infradead.org,
        Jerry Hoemann <jerry.hoemann@....com>,
        Baoquan He <bhe@...hat.com>, Randy Wright <rwright@....com>,
        Dave Young <dyoung@...hat.com>,
        Myron Stowe <myron.stowe@...hat.com>
Subject: Re: [RFC PATCH] PCI, kdump: Clear bus master bit upon shutdown in
 kdump kernel

I looked at this some more. Looks like we do not clear irqs when we do
a kexec reboot. And, the bootup code maintains the same table for the
kexec-ed kernel. I'm looking at the following code in
intel_irq_remapping.c:

        if (ir_pre_enabled(iommu)) {
                if (!is_kdump_kernel()) {
                        pr_warn("IRQ remapping was enabled on %s but
we are not in kdump mode\n",
                                iommu->name);
                        clear_ir_pre_enabled(iommu);
                        iommu_disable_irq_remapping(iommu);
                } else if (iommu_load_old_irte(iommu))
                        pr_err("Failed to copy IR table for %s from
previous kernel\n",
                               iommu->name);
                else
                        pr_info("Copied IR table for %s from previous kernel\n",
                                iommu->name);
        }

Would cleaning the interrupts(like in the non kdump path above) just
before shutdown help here? This should clear the interrupts enabled
for all the devices in the current kernel. So when kdump kernel
starts, it starts clean. This should probably help block out the
interrupts from a device that does not have a driver.

-Deepa