From: Robin Murphy <robin.murphy@arm.com>
To: Kunkun Jiang <jiangkunkun@huawei.com>,
Will Deacon <will@kernel.org>,
Linux IOMMU <iommu@lists.linux-foundation.org>,
open list <linux-kernel@vger.kernel.org>
Cc: wanghaibin.wang@huawei.com, Zenghui Yu <yuzenghui@huawei.com>,
Keqian Zhu <zhukeqian1@huawei.com>
Subject: Re: [question] Assign multiple devices from different SMMUs to a arm_smmu_domain
Date: Tue, 7 Sep 2021 10:43:05 +0100 [thread overview]
Message-ID: <202f32cd-8036-563e-028b-781b999766be@arm.com> (raw)
In-Reply-To: <bbfcb875-0da1-c303-ed48-fdaa890c89b3@huawei.com>
On 2021-09-07 08:41, Kunkun Jiang wrote:
> Hi all,
>
> I am working on VFIO DMA dirty pages tracking based on ARM SMMU HTTU,
> and have done a lot of testing.In the test, I found a problem that
> greatly affects
> performance of VFIO DMA dirty pages tracking.
>
> According to the current arm-smmu-v3 driver, multiple VFIO pass-through
> device comes from different SMMUs will be assigned to different
> arm_smmu_domain. It will create page table for each arm_smmu_domain,
> even though these page tables are exactly the same. Bacause dirty pages
> tracking needs to traverse the page table, multiple page tables will make
> performance worse.
>
> I learned the ARM SMMUv3 spec and had some exchanges with my colleagues
> who work on SMMU hardware. I did not find the restriction that multiple
> SMMUs cannot share the same page table. We migth be able to do this like
> x86 IOMMU. If I have missed something, please point it out.
Sure, it's not impossible, there are just a lot of fiddly
considerations, mostly around how to handle SMMU instances with
different capabilities. We haven't had a strong need to support this
case so far, so we've simply been avoiding all that complexity.
Robin.
> Looking forward to your suggestions.😁
>
> Thanks,
> Kunkun Jiang
>
next prev parent reply other threads:[~2021-09-07 9:43 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-07 7:41 [question] Assign multiple devices from different SMMUs to a arm_smmu_domain Kunkun Jiang
2021-09-07 9:43 ` Robin Murphy [this message]
2021-09-08 5:06 ` Kunkun Jiang
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