KVM ARM Archive on lore.kernel.org
 help / color / Atom feed
From: Jean-Philippe Brucker <jean-philippe@linaro.org>
To: Xiang Zheng <zhengxiang9@huawei.com>
Cc: maz@kernel.org, iommu@lists.linux-foundation.org,
	wangzhou1@hisilicon.com, prime.zeng@hisilicon.com,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC] Use SMMU HTTU for DMA dirty page tracking
Date: Fri, 22 May 2020 19:14:52 +0200
Message-ID: <20200522171452.GC3453945@myrica> (raw)
In-Reply-To: <b926ec0b-fe87-0792-c41d-acad56c656a4@huawei.com>

Hi,

On Tue, May 19, 2020 at 05:42:55PM +0800, Xiang Zheng wrote:
> Hi all,
> 
> Is there any plan for enabling SMMU HTTU?

Not outside of SVA, as far as I know.

> I have seen the patch locates in the SVA series patch, which adds
> support for HTTU:
>     https://www.spinics.net/lists/arm-kernel/msg798694.html
> 
> HTTU reduces the number of access faults on SMMU fault queue
> (permission faults also benifit from it).
> 
> Besides reducing the faults, HTTU also helps to track dirty pages for
> device DMA. Is it feasible to utilize HTTU to get dirty pages on device
> DMA during VFIO live migration?

As you know there is a VFIO interface for this under discussion:
https://lore.kernel.org/kvm/1589781397-28368-1-git-send-email-kwankhede@nvidia.com/
It doesn't implement an internal API to communicate with the IOMMU driver
about dirty pages.

> If SMMU can track dirty pages, devices are not required to implement
> additional dirty pages tracking to support VFIO live migration.

It seems feasible, though tracking it in the device might be more
efficient. I might have misunderstood but I think for live migration of
the Intel NIC they trap guest accesses to the device and introspect its
state to figure out which pages it is accessing.

With HTTU I suppose (without much knowledge about live migration) that
you'd need several new interfaces to the IOMMU drivers:

* A way for VFIO to query HTTU support in the SMMU. There are some
  discussions about communicating more IOMMU capabilities through VFIO but
  no implementation yet. When HTTU isn't supported the DIRTY_PAGES bitmap
  would report all pages as they do now.

* VFIO_IOMMU_DIRTY_PAGES_FLAG_START/STOP would clear the dirty bit
  for all VFIO mappings (which is going to take some time). There is a
  walker in io-pgtable for iova_to_phys() which could be extended. I
  suppose it's also possible to atomically switch the HA and HD bits in
  context descriptors.

* VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP would query the dirty bit for all
  VFIO mappings.

Thanks,
Jean
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

  reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-19  9:42 Xiang Zheng
2020-05-22 17:14 ` Jean-Philippe Brucker [this message]
2020-05-25 11:34   ` Xiang Zheng
2020-05-27  3:27     ` Tian, Kevin
2020-05-27  6:45       ` Xiang Zheng
2020-05-27  8:40         ` Tian, Kevin
2020-05-27  9:14           ` Jean-Philippe Brucker
2020-05-27  6:46     ` Zengtao (B)

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200522171452.GC3453945@myrica \
    --to=jean-philippe@linaro.org \
    --cc=iommu@lists.linux-foundation.org \
    --cc=kvmarm@lists.cs.columbia.edu \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=maz@kernel.org \
    --cc=prime.zeng@hisilicon.com \
    --cc=wangzhou1@hisilicon.com \
    --cc=will@kernel.org \
    --cc=zhengxiang9@huawei.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

KVM ARM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvmarm/0 kvmarm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvmarm kvmarm/ https://lore.kernel.org/kvmarm \
		kvmarm@lists.cs.columbia.edu
	public-inbox-index kvmarm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/edu.columbia.cs.lists.kvmarm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git