From: Jean-Philippe Brucker <jean-philippe@linaro.org>
To: Auger Eric <eric.auger@redhat.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
"Raj, Ashok" <ashok.raj@intel.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>,
"stefanha@gmail.com" <stefanha@gmail.com>,
"Sun, Yi Y" <yi.y.sun@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
Robin Murphy <robin.murphy@arm.com>, "Wu, Hao" <hao.wu@intel.com>,
Will Deacon <will@kernel.org>,
"Tian, Jun J" <jun.j.tian@intel.com>
Subject: Re: [PATCH v5 03/15] iommu/smmu: Report empty domain nesting info
Date: Fri, 17 Jul 2020 11:09:00 +0200 [thread overview]
Message-ID: <20200717090900.GC4850@myrica> (raw)
In-Reply-To: <f3779a69-0295-d668-5f2f-746b6ff2bdce@redhat.com>
On Thu, Jul 16, 2020 at 10:38:17PM +0200, Auger Eric wrote:
> Hi Jean,
>
> On 7/16/20 5:39 PM, Jean-Philippe Brucker wrote:
> > On Tue, Jul 14, 2020 at 10:12:49AM +0000, Liu, Yi L wrote:
> >>> Have you verified that this doesn't break the existing usage of
> >>> DOMAIN_ATTR_NESTING in drivers/vfio/vfio_iommu_type1.c?
> >>
> >> I didn't have ARM machine on my hand. But I contacted with Jean
> >> Philippe, he confirmed no compiling issue. I didn't see any code
> >> getting DOMAIN_ATTR_NESTING attr in current drivers/vfio/vfio_iommu_type1.c.
> >> What I'm adding is to call iommu_domai_get_attr(, DOMAIN_ATTR_NESTIN)
> >> and won't fail if the iommu_domai_get_attr() returns 0. This patch
> >> returns an empty nesting info for DOMAIN_ATTR_NESTIN and return
> >> value is 0 if no error. So I guess it won't fail nesting for ARM.
> >
> > I confirm that this series doesn't break the current support for
> > VFIO_IOMMU_TYPE1_NESTING with an SMMUv3. That said...
> >
> > If the SMMU does not support stage-2 then there is a change in behavior
> > (untested): after the domain is silently switched to stage-1 by the SMMU
> > driver, VFIO will now query nesting info and obtain -ENODEV. Instead of
> > succeding as before, the VFIO ioctl will now fail. I believe that's a fix
> > rather than a regression, it should have been like this since the
> > beginning. No known userspace has been using VFIO_IOMMU_TYPE1_NESTING so
> > far, so I don't think it should be a concern.
> But as Yi mentioned ealier, in the current vfio code there is no
> DOMAIN_ATTR_NESTING query yet.
That's why something that would have succeeded before will now fail:
Before this series, if user asked for a VFIO_IOMMU_TYPE1_NESTING, it would
have succeeded even if the SMMU didn't support stage-2, as the driver
would have silently fallen back on stage-1 mappings (which work exactly
the same as stage-2-only since there was no nesting supported). After the
series, we do check for DOMAIN_ATTR_NESTING so if user asks for
VFIO_IOMMU_TYPE1_NESTING and the SMMU doesn't support stage-2, the ioctl
fails.
I believe it's a good fix and completely harmless, but wanted to make sure
no one objects because it's an ABI change.
Thanks,
Jean
> In my SMMUV3 nested stage series, I added
> such a query in vfio-pci.c to detect if I need to expose a fault region
> but I already test both the returned value and the output arg. So to me
> there is no issue with that change.
> >
> > And if userspace queries the nesting properties using the new ABI
> > introduced in this patchset, it will obtain an empty struct. I think
> > that's acceptable, but it may be better to avoid adding the nesting cap if
> > @format is 0?
> agreed
>
> Thanks
>
> Eric
> >
> > Thanks,
> > Jean
> >
> >>
> >> @Eric, how about your opinion? your dual-stage vSMMU support may
> >> also share the vfio_iommu_type1.c code.
> >>
> >> Regards,
> >> Yi Liu
> >>
> >>> Will
> >
>
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2020-07-17 9:09 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-12 11:20 [PATCH v5 00/15] vfio: expose virtual Shared Virtual Addressing to VMs Liu Yi L
2020-07-12 11:20 ` [PATCH v5 01/15] vfio/type1: Refactor vfio_iommu_type1_ioctl() Liu Yi L
2020-07-12 11:20 ` [PATCH v5 02/15] iommu: Report domain nesting info Liu Yi L
2020-07-17 16:29 ` Auger Eric
2020-07-20 7:20 ` Liu, Yi L
2020-07-12 11:20 ` [PATCH v5 03/15] iommu/smmu: Report empty " Liu Yi L
2020-07-13 13:14 ` Will Deacon
2020-07-14 10:12 ` Liu, Yi L
2020-07-16 15:39 ` Jean-Philippe Brucker
2020-07-16 20:38 ` Auger Eric
2020-07-17 9:09 ` Jean-Philippe Brucker [this message]
2020-07-17 10:28 ` Auger Eric
2020-07-23 9:44 ` Liu, Yi L
2020-07-23 9:40 ` Liu, Yi L
2020-07-17 17:18 ` Auger Eric
2020-07-20 7:26 ` Liu, Yi L
2020-07-12 11:20 ` [PATCH v5 04/15] vfio/type1: Report iommu nesting info to userspace Liu Yi L
2020-07-17 17:34 ` Auger Eric
2020-07-20 7:51 ` Liu, Yi L
2020-07-20 8:33 ` Auger Eric
2020-07-20 8:51 ` Liu, Yi L
2020-07-12 11:21 ` [PATCH v5 05/15] vfio: Add PASID allocation/free support Liu Yi L
2020-07-19 15:38 ` Auger Eric
2020-07-20 8:03 ` Liu, Yi L
2020-07-20 8:26 ` Auger Eric
2020-07-20 8:49 ` Liu, Yi L
2020-07-12 11:21 ` [PATCH v5 06/15] iommu/vt-d: Support setting ioasid set to domain Liu Yi L
2020-07-19 15:38 ` Auger Eric
2020-07-20 8:11 ` Liu, Yi L
2020-07-12 11:21 ` [PATCH v5 07/15] vfio/type1: Add VFIO_IOMMU_PASID_REQUEST (alloc/free) Liu Yi L
2020-07-19 15:38 ` Auger Eric
2020-07-20 8:56 ` Liu, Yi L
2020-07-12 11:21 ` [PATCH v5 08/15] iommu: Pass domain to sva_unbind_gpasid() Liu Yi L
2020-07-19 15:37 ` Auger Eric
2020-07-20 9:06 ` Liu, Yi L
2020-07-12 11:21 ` [PATCH v5 09/15] iommu/vt-d: Check ownership for PASIDs from user-space Liu Yi L
2020-07-19 16:06 ` Auger Eric
2020-07-20 10:18 ` Liu, Yi L
2020-07-20 12:37 ` Auger Eric
2020-07-20 12:55 ` Liu, Yi L
2020-07-12 11:21 ` [PATCH v5 10/15] vfio/type1: Support binding guest page tables to PASID Liu Yi L
2020-07-20 9:37 ` Auger Eric
2020-07-20 10:37 ` Liu, Yi L
2020-07-12 11:21 ` [PATCH v5 11/15] vfio/type1: Allow invalidating first-level/stage IOMMU cache Liu Yi L
2020-07-20 9:41 ` Auger Eric
2020-07-20 10:42 ` Liu, Yi L
2020-07-12 11:21 ` [PATCH v5 12/15] vfio/type1: Add vSVA support for IOMMU-backed mdevs Liu Yi L
2020-07-20 12:22 ` Auger Eric
2020-07-23 12:05 ` Liu, Yi L
2020-07-12 11:21 ` [PATCH v5 13/15] vfio/pci: Expose PCIe PASID capability to guest Liu Yi L
2020-07-20 12:35 ` Auger Eric
2020-07-20 13:00 ` Liu, Yi L
2020-07-12 11:21 ` [PATCH v5 14/15] vfio: Document dual stage control Liu Yi L
2020-07-18 13:39 ` Auger Eric
2020-07-25 8:54 ` Liu, Yi L
2020-07-12 11:21 ` [PATCH v5 15/15] iommu/vt-d: Support reporting nesting capability info Liu Yi L
2020-07-17 17:14 ` Auger Eric
2020-07-20 13:33 ` Liu, Yi L
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=20200717090900.GC4850@myrica \
--to=jean-philippe@linaro.org \
--cc=alex.williamson@redhat.com \
--cc=ashok.raj@intel.com \
--cc=eric.auger@redhat.com \
--cc=hao.wu@intel.com \
--cc=iommu@lists.linux-foundation.org \
--cc=jun.j.tian@intel.com \
--cc=kevin.tian@intel.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=robin.murphy@arm.com \
--cc=stefanha@gmail.com \
--cc=will@kernel.org \
--cc=yi.y.sun@intel.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).