[PATCH v2] PCI: Reset PCIe devices to stop ongoing DMA
vgoyal at redhat.com
Wed Jul 31 15:56:23 EDT 2013
On Tue, Jul 30, 2013 at 09:59:16AM -0600, Bjorn Helgaas wrote:
> On Tue, Jul 30, 2013 at 12:09 AM, Takao Indoh
> <indou.takao at jp.fujitsu.com> wrote:
> > (2013/07/29 23:17), Bjorn Helgaas wrote:
> >> On Sun, Jul 28, 2013 at 6:37 PM, Takao Indoh <indou.takao at jp.fujitsu.com> wrote:
> >>> (2013/07/26 2:00), Bjorn Helgaas wrote:
> >>>> My point about IOMMU and PCI initialization order doesn't go away just
> >>>> because it doesn't fit "kdump policy." Having system initialization
> >>>> occur in a logical order is far more important than making kdump work.
> >>> My next plan is as follows. I think this is matched to logical order
> >>> on boot.
> >>> drivers/pci/pci.c
> >>> - Add function to reset bus, for example, pci_reset_bus(struct pci_bus *bus)
> >>> drivers/iommu/intel-iommu.c
> >>> - On initialization, if IOMMU is already enabled, call this bus reset
> >>> function before disabling and re-enabling IOMMU.
> >> I raised this issue because of arches like sparc that enumerate the
> >> IOMMU before the PCI devices that use it. In that situation, I think
> >> you're proposing this:
> >> panic kernel
> >> enable IOMMU
> >> panic
> >> kdump kernel
> >> initialize IOMMU (already enabled)
> >> pci_reset_bus
> >> disable IOMMU
> >> enable IOMMU
> >> enumerate PCI devices
> >> But the problem is that when you call pci_reset_bus(), you haven't
> >> enumerated the PCI devices, so you don't know what to reset.
> > Right, so my idea is adding reset code into "intel-iommu.c". intel-iommu
> > initialization is based on the assumption that enumeration of PCI devices
> > is already done. We can find target device from IOMMU page table instead
> > of scanning all devices in pci tree.
> > Therefore, this idea is only for intel-iommu. Other architectures need
> > to implement their own reset code.
> That's my point. I'm opposed to adding code to PCI when it only
> benefits x86 and we know other arches will need a fundamentally
> different design. I would rather have a design that can work for all
I agree. It makes sense to work on a design which works for all
And that's when I feel that handling this problem at IOMMU level
makes more sense, if we can.
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