Date:   Fri, 30 Jul 2021 09:21:18 +0800
From:   "chenxiang (M)" <chenxiang66@...ilicon.com>
To:     Robin Murphy <robin.murphy@....com>, <joro@...tes.org>,
        <will@...nel.org>
CC:     Maxime Ripard <mripard@...nel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        <linux-kernel@...r.kernel.org>,
        Chunyan Zhang <chunyan.zhang@...soc.com>,
        <dianders@...omium.org>, <iommu@...ts.linux-foundation.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        "linuxarm@...wei.com" <linuxarm@...wei.com>
Subject: Re: [PATCH v2 00/24] iommu: Refactor DMA domain strictness



在 2021/7/29 18:59, Robin Murphy 写道:
> On 2021-07-29 03:55, chenxiang (M) wrote:
>> Hi Robin,
>>
>>
>> 在 2021/7/28 23:58, Robin Murphy 写道:
>>> Hi all,
>>>
>>> Here's v2 where things start to look more realistic, hence the expanded
>>> CC list. The patches are now based on the current iommu/core branch to
>>> take John's iommu_set_dma_strict() cleanup into account.
>>>
>>> The series remiains in two (or possibly 3) logical parts - for people
>>> CC'd on cookie cleanup patches, the later parts should not affect you
>>> since your drivers don't implement non-strict mode anyway; the cleanup
>>> is all pretty straightforward, but please do yell at me if I've managed
>>> to let a silly mistake slip through and broken your driver.
>>>
>>> This time I have also build-tested x86 as well as arm64 :)
>>
>> I have tested those patchset on ARM64 with SMMUV3, and the testcases 
>> are as follows:
>> - Boot with iommu.strict=0, running fio and it works well;
>> - Boot with iommu.strict=1, running fio and it works well;
>> - Change strict mode to lazy mode when building, the change takes 
>> effect;
>> - Boot without iommu.strict(default strict mode), change the sysfs 
>> interface type from DMA to DMA-FQ dynamically during running fio, and 
>> it works well;
>> - Boot without iommu.strict(default strict mode), change the sysfs 
>> interface type from DMA-FQ to DMA dynamically, and it is not allowed 
>> and print "Device or resource busy"
>> (i know it is qualified, and we can change no-strict mode to strict 
>> by unbind the driver -> change the sysfs interface (type)->bind the 
>> driver (tested this and it works well),
>> but i have a small question: is it also possible to change from 
>> DMA-FQ to DMA dynamically? )
>
> As patch #22 mentions, I think it's possible in principle, but it's 
> certainly trickier. When enabling a flush queue, it doesn't matter if 
> it takes a while for other threads to notice that cookie->fq_domain is 
> now set and stop doing synchronous invalidations (and in the SMMU case 
> it seems like there are probably enough dependencies to additionally 
> prevent the io_pgtable quirk being observable before that). However 
> when disabling, we'd need to be absolutely sure that the driver *has* 
> started invalidating strictly before we stop queueing freed IOVAs, 
> plus we need to be absolutely sure that we've stopped queueing freed 
> IOVAs before we attempt to tear down the flush queue itself. I'm not 
> sure off-hand how feasible it would be to put all that synchronisation 
> in the right places without it also impacting normal operation.
>
> Furthermore, as also noted, there doesn't seem to be a good reason for 
> ever actually needing to do that. If a device isn't trusted, it should 
> be given a strict domain *before* any driver has a chance to start 
> doing anything, or your trust model is broken and pretty useless. I 
> can imagine some niche debugging/benchmarking cases where it might 
> help save a bit of effort, but nothing with a strong enough 
> justification to be worth supporting in mainline.

Ok, thanks.

>
>> Anyway, please feel free to add :
>> Tested-by: Xiang Chen <chenxiang66@...ilicon.com>
>
> That's great, thanks!
>
> Robin.
>
>>> Changes in v2:
>>>
>>> - Add iommu_is_dma_domain() helper to abstract flag check (and help
>>>    avoid silly typos like the one in v1).
>>> - Tweak a few commit messages for spelling and (hopefully) clarity.
>>> - Move the iommu_create_device_direct_mappings() update to patch #14
>>>    where it should have been.
>>> - Rewrite patch #20 as a conversion of the now-existing option.
>>> - Clean up the ops->flush_iotlb_all check which is also made redundant
>>>    by the new domain type
>>> - Add patch #24, which is arguably tangential, but it was something I
>>>    spotted during the rebase, so...
>>>
>>> Once again, the whole lot is available on a branch here:
>>>
>>> https://gitlab.arm.com/linux-arm/linux-rm/-/tree/iommu/fq
>>>
>>> Thanks,
>>> Robin.
>>>
>>>
>>> CC: Marek Szyprowski <m.szyprowski@...sung.com>
>>> CC: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
>>> CC: Geert Uytterhoeven <geert+renesas@...der.be>
>>> CC: Yong Wu <yong.wu@...iatek.com>
>>> CC: Heiko Stuebner <heiko@...ech.de>
>>> CC: Chunyan Zhang <chunyan.zhang@...soc.com>
>>> CC: Chunyan Zhang <chunyan.zhang@...soc.com>
>>> CC: Maxime Ripard <mripard@...nel.org>
>>> CC: Jean-Philippe Brucker <jean-philippe@...aro.org>
>>>
>>> Robin Murphy (24):
>>>    iommu: Pull IOVA cookie management into the core
>>>    iommu/amd: Drop IOVA cookie management
>>>    iommu/arm-smmu: Drop IOVA cookie management
>>>    iommu/vt-d: Drop IOVA cookie management
>>>    iommu/exynos: Drop IOVA cookie management
>>>    iommu/ipmmu-vmsa: Drop IOVA cookie management
>>>    iommu/mtk: Drop IOVA cookie management
>>>    iommu/rockchip: Drop IOVA cookie management
>>>    iommu/sprd: Drop IOVA cookie management
>>>    iommu/sun50i: Drop IOVA cookie management
>>>    iommu/virtio: Drop IOVA cookie management
>>>    iommu/dma: Unexport IOVA cookie management
>>>    iommu/dma: Remove redundant "!dev" checks
>>>    iommu: Introduce explicit type for non-strict DMA domains
>>>    iommu/amd: Prepare for multiple DMA domain types
>>>    iommu/arm-smmu: Prepare for multiple DMA domain types
>>>    iommu/vt-d: Prepare for multiple DMA domain types
>>>    iommu: Express DMA strictness via the domain type
>>>    iommu: Expose DMA domain strictness via sysfs
>>>    iommu: Merge strictness and domain type configs
>>>    iommu/dma: Factor out flush queue init
>>>    iommu: Allow enabling non-strict mode dynamically
>>>    iommu/arm-smmu: Allow non-strict in pgtable_quirks interface
>>>    iommu: Only log strictness for DMA domains
>>>
>>>   .../ABI/testing/sysfs-kernel-iommu_groups     |  2 +
>>>   drivers/iommu/Kconfig                         | 80 
>>> +++++++++----------
>>>   drivers/iommu/amd/iommu.c                     | 21 +----
>>>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   | 25 ++++--
>>>   drivers/iommu/arm/arm-smmu/arm-smmu.c         | 29 ++++---
>>>   drivers/iommu/arm/arm-smmu/qcom_iommu.c       |  8 --
>>>   drivers/iommu/dma-iommu.c                     | 44 +++++-----
>>>   drivers/iommu/exynos-iommu.c                  | 18 +----
>>>   drivers/iommu/intel/iommu.c                   | 23 ++----
>>>   drivers/iommu/iommu.c                         | 53 +++++++-----
>>>   drivers/iommu/ipmmu-vmsa.c                    | 27 +------
>>>   drivers/iommu/mtk_iommu.c                     |  6 --
>>>   drivers/iommu/rockchip-iommu.c                | 11 +--
>>>   drivers/iommu/sprd-iommu.c                    |  6 --
>>>   drivers/iommu/sun50i-iommu.c                  | 12 +--
>>>   drivers/iommu/virtio-iommu.c                  |  8 --
>>>   include/linux/dma-iommu.h                     |  9 ++-
>>>   include/linux/iommu.h                         | 15 +++-
>>>   18 files changed, 171 insertions(+), 226 deletions(-)
>>>
>>
>>
>
> .
>

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