From: Lu Baolu <baolu.lu@linux.intel.com>
To: Christoph Hellwig <hch@lst.de>
Cc: baolu.lu@linux.intel.com, Joerg Roedel <joro@8bytes.org>,
ashok.raj@intel.com, jacob.jun.pan@linux.intel.com,
kevin.tian@intel.com, iommu@lists.linux-foundation.org,
linux-kernel@vger.kernel.org, Daniel Drake <drake@endlessm.com>,
Derrick Jonathan <jonathan.derrick@intel.com>,
Jerry Snitselaar <jsnitsel@redhat.com>,
Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH 3/6] iommu/vt-d: Don't force 32bit devices to uses DMA domain
Date: Sun, 8 Mar 2020 10:15:48 +0800 [thread overview]
Message-ID: <b86e2bce-9907-05d0-b937-4b120797ba06@linux.intel.com> (raw)
In-Reply-To: <20200307142144.GB26190@lst.de>
Hi Christoph,
On 2020/3/7 22:21, Christoph Hellwig wrote:
> On Sat, Mar 07, 2020 at 02:20:11PM +0800, Lu Baolu wrote:
>> Currently, if a 32bit device initially uses an identity domain,
>> Intel IOMMU driver will convert it forcibly to a DMA one if its
>> address capability is not enough for the whole system memory.
>> The motivation was to overcome the overhead caused by possible
>> bounced buffer.
>>
>> Unfortunately, this improvement has led to many problems. For
>> example, some 32bit devices are required to use an identity
>> domain, forcing them to use DMA domain will cause the device
>> not to work anymore. On the other hand, the VMD sub-devices
>> share a domain but each sub-device might have different address
>> capability. Forcing a VMD sub-device to use DMA domain blindly
>> will impact the operation of other sub-devices without any
>> notification. Further more, PCI aliased devices (PCI bridge
>> and all devices beneath it, VMD devices and various devices
>> quirked with pci_add_dma_alias()) must use the same domain.
>> Forcing one device to switch to DMA domain during runtime
>> will cause in-fligh DMAs for other devices to abort or target
>> to other memory which might cause undefind system behavior.
>
> I still don't like the idea to enforce either a strict dynamic
> IOMMU mapping or an identify mapping mode.
>
> Can we add a new AUTO domain which will allow using the identity
> mapping when available? That somewhat matches the existing x86
> default, and also what powerpc does.
Sai is proposing a series to change the default domain through sysfs
during runtime.
https://lore.kernel.org/linux-iommu/FFF73D592F13FD46B8700F0A279B802F4FBF7E4B@ORSMSX114.amr.corp.intel.com/T/#mb919da5567da7692ee7058a00a137145adf950a1
It has evolved into v2. Not sure whether it's what you want.
> I have a series to lift
> that bypass mode into the core dma-mapping code that I need
> to repost, which I think would be suitable for intel-iommu as well.
>
Looking forward to your repost.
Best regards,
baolu
next prev parent reply other threads:[~2020-03-08 2:15 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-07 6:20 [PATCH 0/6] Replace private domain with per-group default Lu Baolu
2020-03-07 6:20 ` [PATCH 1/6] iommu: Add dev_def_domain_type() callback in iommu_ops Lu Baolu
2020-03-07 14:18 ` Christoph Hellwig
2020-03-08 2:08 ` Lu Baolu
2020-03-07 6:20 ` [PATCH 2/6] iommu: Configure default domain with dev_def_domain_type Lu Baolu
2020-03-07 6:20 ` [PATCH 3/6] iommu/vt-d: Don't force 32bit devices to uses DMA domain Lu Baolu
2020-03-07 14:21 ` Christoph Hellwig
2020-03-08 2:15 ` Lu Baolu [this message]
2020-03-10 10:58 ` Joerg Roedel
2020-03-07 6:20 ` [PATCH 4/6] iommu/vt-d: Don't force PCI sub-hierarchy to use " Lu Baolu
2020-03-07 6:20 ` [PATCH 5/6] iommu/vt-d: Add dev_def_domain_type callback Lu Baolu
2020-03-07 6:20 ` [PATCH 6/6] iommu/vt-d: Apply per-device dma_ops Lu Baolu
2020-03-10 11:15 ` [PATCH 0/6] Replace private domain with per-group default Joerg Roedel
2020-03-11 6:50 ` Lu Baolu
2020-03-13 13:36 ` Joerg Roedel
2020-03-14 1:13 ` Lu Baolu
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