linux-kernel - Re: [PATCH] pci, dmar: Update dmar units devices list during hotplug

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Date:	Thu, 19 May 2011 16:15:08 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-pci@...r.kernel.org, iommu@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pci, dmar: Update dmar units devices list during
 hotplug

On Sun, 2011-05-08 at 11:48 -0700, Yinghai Lu wrote:
> When do pci remove/rescan on system that have more iommus, got
> 
> [  894.089745] Set context mapping for c4:00.0
> [  894.110890] mpt2sas3: Allocated physical memory: size(4293 kB)
> [  894.112556] mpt2sas3: Current Controller Queue Depth(1883), Max Controller Queue Depth(2144)
> [  894.127278] mpt2sas3: Scatter Gather Elements per IO(128)
> [  894.361295] DRHD: handling fault status reg 2
> [  894.364053] DMAR:[DMA Read] Request device [c4:00.0] fault addr fffbe000
> [  894.364056] DMAR:[fault reason 02] Present bit in context entry is cl
> 
> it turns out when remove/rescan, pci dev will be freed and will get another new dev.
> but drhd units still keep old one... so dmar_find_matched_drhd_unit will
> return wrong drhd and iommu for the device that is not on first iommu.
> 
> So need to update devices in drhd_units during pci remove/rescan.
> 
> Could save domain/bus/device/function aside in the list and according that info
> restore new dev to drhd_units later.
> Then dmar_find_matched_drdh_unit and device_to_iommu could return right drhd and iommu.

I think I'd vote for saving some kind of representation of the bus
hierarchy, we probably don't need to list every possible individual
device.  Leaving a broken pointer around to be matched up and restored
later just seems like a continuation of an idea that was bad to begin
with.  Thanks,

Alex

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