From: Lu Baolu <baolu.lu@linux.intel.com>
To: John Garry <john.garry@huawei.com>,
Joerg Roedel <joro@8bytes.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Bjorn Helgaas <bhelgaas@google.com>
Cc: baolu.lu@linux.intel.com, kevin.tian@intel.com,
ashok.raj@intel.com, linux-kernel@vger.kernel.org,
iommu@lists.linux-foundation.org, jacob.jun.pan@intel.com,
Robin Murphy <robin.murphy@arm.com>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [RFC PATCH 0/4] iommu: Per-group default domain type
Date: Tue, 21 Jan 2020 08:43:52 +0800 [thread overview]
Message-ID: <f417cd0b-1bf7-7da2-3a64-b8b74b03da02@linux.intel.com> (raw)
In-Reply-To: <ba7a7e6a-8b23-fca0-a8bb-72c4dbfa8390@huawei.com>
Hi John,
On 1/20/20 5:44 PM, John Garry wrote:
> On 01/01/2020 05:26, Lu Baolu wrote:
>> An IOMMU group represents the smallest set of devices that are considered
>> to be isolated. All devices belonging to an IOMMU group share a default
>> domain for DMA APIs. There are two types of default domain:
>> IOMMU_DOMAIN_DMA
>> and IOMMU_DOMAIN_IDENTITY. The former means IOMMU translation, while the
>> latter means IOMMU by-pass.
>>
>> Currently, the default domain type for the IOMMU groups is determined
>> globally. All IOMMU groups use a single default domain type. The global
>> default domain type can be adjusted by kernel build configuration or
>> kernel parameters.
>>
>> More and more users are looking forward to a fine grained default domain
>> type. For example, with the global default domain type set to
>> translation,
>> the OEM verndors or end users might want some trusted and fast-speed
>> devices
>> to bypass IOMMU for performance gains. On the other hand, with global
>> default domain type set to by-pass, some devices with limited system
>> memory addressing capability might want IOMMU translation to remove the
>> bounce buffer overhead.
>
> Hi Lu Baolu,
>
> Do you think that it would be a more common usecase to want
> kernel-managed devices to be passthrough for performance reasons and
> some select devices to be in DMA domain, like those with limited address
> cap or whose drivers request huge amounts of memory?
>
> I just think it would be more manageable to set kernel commandline
> parameters for this, i.e. those select few which want DMA domain.
>
It's just two sides of a coin. Currently, iommu subsystem make DMA
domain by default, that's the reason why I selected to let user set
which devices are willing to use identity domains.
> Thanks,
> John
Best regards,
baolu
next prev parent reply other threads:[~2020-01-21 0:45 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-01 5:26 [RFC PATCH 0/4] iommu: Per-group default domain type Lu Baolu
2020-01-01 5:26 ` [RFC PATCH 1/4] driver core: Add iommu_passthrough to struct device Lu Baolu
2020-01-01 5:26 ` [RFC PATCH 2/4] PCI: Add "pci=iommu_passthrough=" parameter for iommu passthrough Lu Baolu
2020-01-18 0:18 ` Bjorn Helgaas
2020-01-18 2:04 ` Lu Baolu
2020-01-21 14:17 ` Bjorn Helgaas
2020-01-22 4:49 ` Lu Baolu
2020-01-01 5:26 ` [RFC PATCH 3/4] iommu: Preallocate iommu group when probing devices Lu Baolu
2020-01-17 10:21 ` Joerg Roedel
2020-01-18 2:18 ` Lu Baolu
2020-01-19 6:29 ` Lu Baolu
2020-01-21 12:45 ` Robin Murphy
2020-01-22 5:39 ` Lu Baolu
2020-01-23 14:55 ` Robin Murphy
2020-01-01 5:26 ` [RFC PATCH 4/4] iommu: Determine default domain type before allocating domain Lu Baolu
2020-01-20 9:44 ` [RFC PATCH 0/4] iommu: Per-group default domain type John Garry
2020-01-21 0:43 ` Lu Baolu [this message]
2020-01-21 10:14 ` John Garry
2020-01-22 4:58 ` Lu Baolu
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