linux-kernel - Re: [Patch Part2 V2 15/17] iommu/vt-d, PCI: update DRHD/RMRR/ATSR device scope caches when PCI hotplug happens

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Date:	Mon, 10 Mar 2014 16:46:32 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	David Woodhouse <dwmw2@...radead.org>
CC:	Joerg Roedel <joro@...tes.org>, Yinghai Lu <yinghai@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Vinod Koul <vinod.koul@...el.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Tony Luck <tony.luck@...el.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
	iommu@...ts.linux-foundation.org
Subject: Re: [Patch Part2 V2 15/17] iommu/vt-d, PCI: update DRHD/RMRR/ATSR
 device scope caches when PCI hotplug happens

Hi David,
	Good suggestion! It should make hotplug logic simpler too.
Will try to work out some patches for it.
Thanks!
Gerry

On 2014/3/7 2:25, David Woodhouse wrote:
> On Wed, 2014-02-19 at 14:07 +0800, Jiang Liu wrote:
>> Current Intel DMAR/IOMMU driver assumes that all PCI devices
>> associated
>> with DMAR/RMRR/ATSR device scope arrays are created at boot time and
>> won't change at runtime, so it caches pointers of associated PCI
>> device
>> object. That assumption may be wrong now due to:
>> 1) introduction of PCI host bridge hotplug
>> 2) PCI device hotplug through sysfs interfaces.
> ...
>> This patch introduces a new mechanism to update the DRHD/RMRR/ATSR
>> device scope caches by hooking PCI bus notification.
> 
> Hm, this seems overly complex. Can't we just abandon the
> dmaru->devices[] array completely? In dmar_find_matched_drhd_unit()
> can't we just compare the path in the scope entries directly to the PCI
> device we are trying to find a DRHD for?
> 
> We then cache the result in dev->archdata.iommu for ever (well, until
> hot-unplug) anyway, so it shouldn't even be any less efficient to do it
> on demand, right?
> 
> That's true at least for dmar_find_matched_drhd_unit(). Perhaps we'd
> need to find a way to cache the result for
> dmar_find_matched_atsr_unit()?
> 
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