Re: [RFC][PATCH] Reset PCIe devices to address DMA problem on kdumpwith iommu

From: Takao Indoh
Date: Wed Sep 12 2012 - 05:05:37 EST

(2012/09/11 23:43), Vivek Goyal wrote:
On Tue, Sep 11, 2012 at 07:32:35PM +0900, Takao Indoh wrote:

I'll post new patch which clears bus master bit and resets devices in
second kernel.

As to the boot parameter to enable this function, you suggested using
reset_devices. I found that on a certain platform resetting devices
caused PCIe error due to a hardware bug. Therefore I think we need
new parameter apart from reset_devices to disable this function on
such a machine.

Can you explain a bit more how the error happens. I still don't think
that because of a bug in a platform somewhere we should be introducing
a separate command line parameter and not reuse the exisiting one. Also
you have not explained what's the bug and how a new parameter will
avoid the bug.

The bug I mentioned is that ACS Violation occurs at PCIe switch when
reading PCI configuration after device reset. I got information that
this violation is caused by PCIe switch bug. The machine becomes fatal
status by this error.

The reason why I try to introduce new parameter is that I want to avoid
regression by this patch. Let's say this patch was included in kernel
and its reset function was enabled by reset_devices as you said. AFAIK
reset_devices is always needed for kdump, so it means that devices are
always reset at kdump boot time. It causes a regression that system
always becomes abnormal status when we run kdump on the machine which has
a bug I mentioned.

To avoid this regression, I want to separate reset_devices from this
reset function. Or how about this?
- if user specify reset_devices, devices are reset by this patch, as you
- To avoid a regression I said, add new parameter like "pci=noreset".
If this parameter is specified, the reset function I add is disabled
and we can avoid regression.

Takao Indoh

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