linux-kernel - Re: [PATCH v2] PCI: Reset PCIe devices to stop ongoing DMA

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Date:	Thu, 13 Jun 2013 11:44:49 +0900
From:	Takao Indoh <indou.takao@...fujitsu.com>
To:	bhelgaas@...gle.com
CC:	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	iommu@...ts.linux-foundation.org, kexec@...ts.infradead.org,
	ishii.hironobu@...fujitsu.com, ddutile@...hat.com,
	bill.sumner@...com, alex.williamson@...hat.com, vgoyal@...hat.com,
	hbabu@...ibm.com
Subject: Re: [PATCH v2] PCI: Reset PCIe devices to stop ongoing DMA

(2013/06/12 13:45), Bjorn Helgaas wrote:
> [+cc Vivek, Haren; sorry I didn't think to add you earlier]
> 
> On Tue, Jun 11, 2013 at 12:08 AM, Takao Indoh
> <indou.takao@...fujitsu.com> wrote:
>> (2013/06/11 11:20), Bjorn Helgaas wrote:
> 
>>> I'm not sure you need to reset legacy devices (or non-PCI devices)
>>> yet, but the current hook isn't anchored anywhere -- it's just an
>>> fs_initcall() that doesn't give the reader any clue about the
>>> connection between the reset and the problem it's solving.
>>>
>>> If we do something like this patch, I think it needs to be done at the
>>> point where we enable or disable the IOMMU.  That way, it's connected
>>> to the important event, and there's a clue about how to make
>>> corresponding fixes for other IOMMUs.
>>
>> Ok. pci_iommu_init() is appropriate place to add this hook?
> 
> I looked at various IOMMU init places today, and it's far more
> complicated and varied than I had hoped.
> 
> This reset scheme depends on enumerating PCI devices before we
> initialize the IOMMU used by those devices.  x86 works that way today,
> but not all architectures do (see the sparc pci_fire_pbm_init(), for

Sorry, could you tell me which part depends on architecture?

> example).  And I think conceptually, the IOMMU should be enumerated
> and initialized *before* the devices that use it.
> 
> So I'm uncomfortable with that aspect of this scheme.
> 
> It would be at least conceivable to reset the devices in the system
> kernel, before the kexec.  I know we want to do as little as possible
> in the crashing kernel, but it's at least a possibility, and it might
> be cleaner.

I bet this will be not accepted by kdump maintainer. Everything in panic
kernel is unreliable.

Thanks,
Takao Indoh

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