From: "Tian, Kevin" <kevin.tian@intel.com>
To: Keqian Zhu <zhukeqian1@huawei.com>,
Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc: "Sun, Yi Y" <yi.y.sun@intel.com>,
"Zhao, Yan Y" <yan.y.zhao@intel.com>,
"maz@kernel.org" <maz@kernel.org>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>,
Kirti Wankhede <kwankhede@nvidia.com>,
"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
"prime.zeng@hisilicon.com" <prime.zeng@hisilicon.com>,
Will Deacon <will@kernel.org>,
"kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: RE: [RFC] Use SMMU HTTU for DMA dirty page tracking
Date: Fri, 5 Feb 2021 05:21:20 +0000 [thread overview]
Message-ID: <MWHPR11MB18869021F6B6F66BD71346C88CB29@MWHPR11MB1886.namprd11.prod.outlook.com> (raw)
In-Reply-To: <c1c96639-2311-398a-15e0-2ff2d59fe320@huawei.com>
> From: Keqian Zhu <zhukeqian1@huawei.com>
> Sent: Friday, February 5, 2021 11:31 AM
>
> Hi Jean and Kevin,
>
> FYI, I have send out the SMMUv3 HTTU support for DMA dirty tracking[1] a
> week ago.
>
> Thanks,
> Keqian
>
> [1] https://lore.kernel.org/linux-iommu/20210128151742.18840-1-
> zhukeqian1@huawei.com/
Thanks for the pointer. We will take a look.
>
> On 2020/5/27 17:14, Jean-Philippe Brucker wrote:
> > On Wed, May 27, 2020 at 08:40:47AM +0000, Tian, Kevin wrote:
> >>> From: Xiang Zheng <zhengxiang9@huawei.com>
> >>> Sent: Wednesday, May 27, 2020 2:45 PM
> >>>
> >>>
> >>> On 2020/5/27 11:27, Tian, Kevin wrote:
> >>>>> From: Xiang Zheng
> >>>>> Sent: Monday, May 25, 2020 7:34 PM
> >>>>>
> >>>>> [+cc Kirti, Yan, Alex]
> >>>>>
> >>>>> On 2020/5/23 1:14, Jean-Philippe Brucker wrote:
> >>>>>> 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.
> >>>>
> >>>> We plan to add such API later, e.g. to utilize A/D bit in VT-d 2nd-level
> >>>> page tables (Rev 3.0).
> >>>>
> >>>
> >>> Thank you, Kevin.
> >>>
> >>> When will you send this series patches? Maybe(Hope) we can also
> support
> >>> hardware-based dirty pages tracking via common APIs based on your
> >>> patches. :)
> >>
> >> Yan is working with Kirti on basic live migration support now. After that
> >> part is done, we will start working on A/D bit support. Yes, common APIs
> >> are definitely the goal here.
> >>
> >>>
> >>>>>
> >>>>>>
> >>>>>>> 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.
> >>>>
> >>>> Does HTTU implement A/D-like mechanism in SMMU page tables, or
> just
> >>>> report dirty pages in a log buffer? Either way tracking dirty pages in
> IOMMU
> >>>> side is generic thus doesn't require device-specific tweak like in Intel NIC.
> >>>>
> >>>
> >>> Currently HTTU just implement A/D-like mechanism in SMMU page
> tables.
> >>> We certainly
> >>> expect SMMU can also implement PML-like feature so that we can avoid
> >>> walking the
> >>> whole page table to get the dirty pages.
> >
> > There is no reporting of dirty pages in log buffer. It might be possible
> > to do software logging based on PRI or Stall, but that requires special
> > support in the endpoint as well as the SMMU.
> >
> >> Is there a link to HTTU introduction?
> >
> > I don't know any gentle introduction, but there are sections D5.4.11
> > "Hardware management of the Access flag and dirty state" in the ARM
> > Architecture Reference Manual (DDI0487E), and section 3.13 "Translation
> > table entries and Access/Dirty flags" in the SMMU specification
> > (IHI0070C). HTTU stands for "Hardware Translation Table Update".
> >
> > In short, when HTTU is enabled, the SMMU translation performs an atomic
> > read-modify-write on the leaf translation table descriptor, setting some
> > bits depending on the type of memory access. This can be enabled
> > independently on both stage-1 and stage-2 tables (equivalent to your 1st
> > and 2nd page tables levels, I think).
> >
> > Thanks,
> > Jean
> > _______________________________________________
> > kvmarm mailing list
> > kvmarm@lists.cs.columbia.edu
> > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
> > .
> >
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2021-02-05 5:21 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <b926ec0b-fe87-0792-c41d-acad56c656a4@huawei.com>
2020-05-22 17:14 ` [RFC] Use SMMU HTTU for DMA dirty page tracking Jean-Philippe Brucker
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
2021-02-05 3:30 ` Keqian Zhu
2021-02-05 5:21 ` Tian, Kevin [this message]
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=MWHPR11MB18869021F6B6F66BD71346C88CB29@MWHPR11MB1886.namprd11.prod.outlook.com \
--to=kevin.tian@intel.com \
--cc=alex.williamson@redhat.com \
--cc=iommu@lists.linux-foundation.org \
--cc=jean-philippe@linaro.org \
--cc=kvmarm@lists.cs.columbia.edu \
--cc=kwankhede@nvidia.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=maz@kernel.org \
--cc=prime.zeng@hisilicon.com \
--cc=will@kernel.org \
--cc=yan.y.zhao@intel.com \
--cc=yi.y.sun@intel.com \
--cc=zhukeqian1@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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).