From: Alex Williamson <alex.williamson@redhat.com>
To: "Liu, Yi L" <yi.l.liu@intel.com>
Cc: "jean-philippe@linaro.org" <jean-philippe@linaro.org>,
"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>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Sun, Yi Y" <yi.y.sun@intel.com>, "Wu, Hao" <hao.wu@intel.com>,
"Tian, Jun J" <jun.j.tian@intel.com>
Subject: Re: [PATCH v3 06/14] vfio/type1: Add VFIO_IOMMU_PASID_REQUEST (alloc/free)
Date: Thu, 9 Jul 2020 08:27:51 -0600 [thread overview]
Message-ID: <20200709082751.320742ab@x1.home> (raw)
In-Reply-To: <DM5PR11MB143584D5A0AAE13E0D2D04B7C3640@DM5PR11MB1435.namprd11.prod.outlook.com>
On Thu, 9 Jul 2020 07:16:31 +0000
"Liu, Yi L" <yi.l.liu@intel.com> wrote:
> Hi Alex,
>
> After more thinking, looks like adding a r-b tree is still not enough to
> solve the potential problem for free a range of PASID in one ioctl. If
> caller gives [0, MAX_UNIT] in the free request, kernel anyhow should
> loop all the PASIDs and search in the r-b tree. Even VFIO can track the
> smallest/largest allocated PASID, and limit the free range to an accurate
> range, it is still no efficient. For example, user has allocated two PASIDs
> ( 1 and 999), and user gives the [0, MAX_UNIT] range in free request. VFIO
> will limit the free range to be [1, 999], but still needs to loop PASID 1 -
> 999, and search in r-b tree.
That sounds like a poor tree implementation. Look at vfio_find_dma()
for instance, it returns a node within the specified range. If the
tree has two nodes within the specified range we should never need to
call a search function like vfio_find_dma() more than three times. We
call it once, get the first node, remove it. Call it again, get the
other node, remove it. Call a third time, find no matches, we're done.
So such an implementation limits searches to N+1 where N is the number
of nodes within the range.
> So I'm wondering can we fall back to prior proposal which only free one
> PASID for a free request. how about your opinion?
Doesn't it still seem like it would be a useful user interface to have
a mechanism to free all pasids, by calling with exactly [0, MAX_UINT]?
I'm not sure if there's another use case for this given than the user
doesn't have strict control of the pasid values they get. Thanks,
Alex
> > From: Liu, Yi L <yi.l.liu@intel.com>
> > Sent: Thursday, July 9, 2020 10:26 AM
> >
> > Hi Kevin,
> >
> > > From: Tian, Kevin <kevin.tian@intel.com>
> > > Sent: Thursday, July 9, 2020 10:18 AM
> > >
> > > > From: Liu, Yi L <yi.l.liu@intel.com>
> > > > Sent: Thursday, July 9, 2020 10:08 AM
> > > >
> > > > Hi Kevin,
> > > >
> > > > > From: Tian, Kevin <kevin.tian@intel.com>
> > > > > Sent: Thursday, July 9, 2020 9:57 AM
> > > > >
> > > > > > From: Liu, Yi L <yi.l.liu@intel.com>
> > > > > > Sent: Thursday, July 9, 2020 8:32 AM
> > > > > >
> > > > > > Hi Alex,
> > > > > >
> > > > > > > Alex Williamson <alex.williamson@redhat.com>
> > > > > > > Sent: Thursday, July 9, 2020 3:55 AM
> > > > > > >
> > > > > > > On Wed, 8 Jul 2020 08:16:16 +0000 "Liu, Yi L"
> > > > > > > <yi.l.liu@intel.com> wrote:
> > > > > > >
> > > > > > > > Hi Alex,
> > > > > > > >
> > > > > > > > > From: Liu, Yi L < yi.l.liu@intel.com>
> > > > > > > > > Sent: Friday, July 3, 2020 2:28 PM
> > > > > > > > >
> > > > > > > > > Hi Alex,
> > > > > > > > >
> > > > > > > > > > From: Alex Williamson <alex.williamson@redhat.com>
> > > > > > > > > > Sent: Friday, July 3, 2020 5:19 AM
> > > > > > > > > >
> > > > > > > > > > On Wed, 24 Jun 2020 01:55:19 -0700 Liu Yi L
> > > > > > > > > > <yi.l.liu@intel.com> wrote:
> > > > > > > > > >
> > > > > > > > > > > This patch allows user space to request PASID
> > > > > > > > > > > allocation/free,
> > > > e.g.
> > > > > > > > > > > when serving the request from the guest.
> > > > > > > > > > >
> > > > > > > > > > > PASIDs that are not freed by userspace are
> > > > > > > > > > > automatically freed
> > > > > > when
> > > > > > > > > > > the IOASID set is destroyed when process exits.
> > > > > > > > [...]
> > > > > > > > > > > +static int vfio_iommu_type1_pasid_request(struct
> > > > > > > > > > > +vfio_iommu
> > > > > > *iommu,
> > > > > > > > > > > + unsigned long arg) {
> > > > > > > > > > > + struct vfio_iommu_type1_pasid_request req;
> > > > > > > > > > > + unsigned long minsz;
> > > > > > > > > > > +
> > > > > > > > > > > + minsz = offsetofend(struct
> > > vfio_iommu_type1_pasid_request,
> > > > > > > range);
> > > > > > > > > > > +
> > > > > > > > > > > + if (copy_from_user(&req, (void __user *)arg, minsz))
> > > > > > > > > > > + return -EFAULT;
> > > > > > > > > > > +
> > > > > > > > > > > + if (req.argsz < minsz || (req.flags &
> > > > > > > ~VFIO_PASID_REQUEST_MASK))
> > > > > > > > > > > + return -EINVAL;
> > > > > > > > > > > +
> > > > > > > > > > > + if (req.range.min > req.range.max)
> > > > > > > > > >
> > > > > > > > > > Is it exploitable that a user can spin the kernel for a
> > > > > > > > > > long time in the case of a free by calling this with [0,
> > > > > > > > > > MAX_UINT] regardless of their
> > > > > > > actual
> > > > > > > > > allocations?
> > > > > > > > >
> > > > > > > > > IOASID can ensure that user can only free the PASIDs
> > > > > > > > > allocated to the
> > > > > > user.
> > > > > > > but
> > > > > > > > > it's true, kernel needs to loop all the PASIDs within the
> > > > > > > > > range provided by user.
> > > > > > > it
> > > > > > > > > may take a long time. is there anything we can do? one
> > > > > > > > > thing may limit
> > > > > > the
> > > > > > > range
> > > > > > > > > provided by user?
> > > > > > > >
> > > > > > > > thought about it more, we have per-VM pasid quota (say
> > > > > > > > 1000), so even if user passed down [0, MAX_UNIT], kernel
> > > > > > > > will only loop the
> > > > > > > > 1000 pasids at most. do you think we still need to do something on it?
> > > > > > >
> > > > > > > How do you figure that? vfio_iommu_type1_pasid_request()
> > > > > > > accepts the user's min/max so long as (max > min) and passes
> > > > > > > that to vfio_iommu_type1_pasid_free(), then to
> > > > > > > vfio_pasid_free_range() which loops as:
> > > > > > >
> > > > > > > ioasid_t pasid = min;
> > > > > > > for (; pasid <= max; pasid++)
> > > > > > > ioasid_free(pasid);
> > > > > > >
> > > > > > > A user might only be able to allocate 1000 pasids, but
> > > > > > > apparently they can ask to free all they want.
> > > > > > >
> > > > > > > It's also not obvious to me that calling ioasid_free() is only
> > > > > > > allowing the user to free their own passid. Does it? It
> > > > > > > would be a pretty
> > > > >
> > > > > Agree. I thought ioasid_free should at least carry a token since
> > > > > the user
> > > > space is
> > > > > only allowed to manage PASIDs in its own set...
> > > > >
> > > > > > > gaping hole if a user could free arbitrary pasids. A r-b tree
> > > > > > > of passids might help both for security and to bound spinning in a loop.
> > > > > >
> > > > > > oh, yes. BTW. instead of r-b tree in VFIO, maybe we can add an
> > > > > > ioasid_set parameter for ioasid_free(), thus to prevent the user
> > > > > > from freeing PASIDs that doesn't belong to it. I remember Jacob
> > > > > > mentioned it
> > > > before.
> > > > > >
> > > > >
> > > > > check current ioasid_free:
> > > > >
> > > > > spin_lock(&ioasid_allocator_lock);
> > > > > ioasid_data = xa_load(&active_allocator->xa, ioasid);
> > > > > if (!ioasid_data) {
> > > > > pr_err("Trying to free unknown IOASID %u\n", ioasid);
> > > > > goto exit_unlock;
> > > > > }
> > > > >
> > > > > Allow an user to trigger above lock paths with MAX_UINT times
> > > > > might still
> > > > be bad.
> > > >
> > > > yeah, how about the below two options:
> > > >
> > > > - comparing the max - min with the quota before calling ioasid_free().
> > > > If max - min > current quota of the user, then should fail it. If
> > > > max - min < quota, then call ioasid_free() one by one. still trigger
> > > > the above lock path with quota times.
> > >
> > > This is definitely wrong. [min, max] is about the range of the PASID
> > > value, while quota is about the number of allocated PASIDs. It's a bit
> > > weird to mix two together.
> >
> > got it.
> >
> > > btw what is the main purpose of allowing batch PASID free requests?
> > > Can we just simplify to allow one PASID in each free just like how is
> > > it done in allocation path?
> >
> > it's an intention to reuse the [min, max] range as allocation path. currently, we
> > don't have such request as far as I can see.
> >
> > > >
> > > > - pass the max and min to ioasid_free(), let ioasid_free() decide. should
> > > > be able to avoid trigger the lock multiple times, and ioasid has have a
> > > > track on how may PASIDs have been allocated, if max - min is larger than
> > > > the allocated number, should fail anyway.
> > >
> > > What about Alex's r-b tree suggestion? Is there any downside in you mind?
> >
> > no downside, I was just wanting to reuse the tracks in ioasid_set. I can add a r-b
> > for allocated PASIDs and find the PASIDs in the r-b tree only do free for the
> > PASIDs found in r-b tree, others in the range would be ignored.
> > does it look good?
> >
> > Regards,
> > Yi Liu
> >
> > > Thanks,
> > > Kevin
>
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next prev parent reply other threads:[~2020-07-09 14:28 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-24 8:55 [PATCH v3 00/14] vfio: expose virtual Shared Virtual Addressing to VMs Liu Yi L
2020-06-24 8:55 ` [PATCH v3 01/14] vfio/type1: Refactor vfio_iommu_type1_ioctl() Liu Yi L
2020-07-02 21:21 ` Alex Williamson
2020-07-03 3:46 ` Liu, Yi L
2020-06-24 8:55 ` [PATCH v3 02/14] iommu: Report domain nesting info Liu Yi L
2020-06-26 7:47 ` Jean-Philippe Brucker
2020-06-26 16:04 ` Robin Murphy
2020-06-27 6:53 ` Liu, Yi L
2020-06-30 1:20 ` Tian, Kevin
2020-06-27 6:14 ` Liu, Yi L
2020-06-29 9:24 ` Stefan Hajnoczi
2020-06-29 12:23 ` Liu, Yi L
2020-06-30 2:00 ` Tian, Kevin
2020-06-30 3:45 ` Liu, Yi L
2020-07-03 9:59 ` Stefan Hajnoczi
2020-07-02 17:54 ` Alex Williamson
2020-07-03 3:53 ` Liu, Yi L
2020-06-24 8:55 ` [PATCH v3 03/14] vfio/type1: Report iommu nesting info to userspace Liu Yi L
2020-07-02 18:38 ` Alex Williamson
2020-07-03 6:05 ` Liu, Yi L
2020-07-03 13:03 ` Liu, Yi L
2020-06-24 8:55 ` [PATCH v3 04/14] vfio: Add PASID allocation/free support Liu Yi L
2020-07-02 21:17 ` Alex Williamson
2020-07-03 6:08 ` Liu, Yi L
2020-06-24 8:55 ` [PATCH v3 05/14] iommu/vt-d: Support setting ioasid set to domain Liu Yi L
2020-06-24 8:55 ` [PATCH v3 06/14] vfio/type1: Add VFIO_IOMMU_PASID_REQUEST (alloc/free) Liu Yi L
2020-07-02 21:18 ` Alex Williamson
2020-07-03 6:28 ` Liu, Yi L
2020-07-08 8:16 ` Liu, Yi L
2020-07-08 19:54 ` Alex Williamson
2020-07-09 0:32 ` Liu, Yi L
2020-07-09 1:56 ` Tian, Kevin
2020-07-09 2:08 ` Liu, Yi L
2020-07-09 2:18 ` Tian, Kevin
2020-07-09 2:26 ` Liu, Yi L
2020-07-09 7:16 ` Liu, Yi L
2020-07-09 14:27 ` Alex Williamson [this message]
2020-07-09 18:05 ` Jacob Pan
2020-07-10 5:39 ` Liu, Yi L
2020-07-10 12:55 ` Alex Williamson
2020-07-10 13:03 ` Liu, Yi L
2020-06-24 8:55 ` [PATCH v3 07/14] iommu: Pass domain to sva_unbind_gpasid() Liu Yi L
2020-06-24 8:55 ` [PATCH v3 08/14] iommu/vt-d: Check ownership for PASIDs from user-space Liu Yi L
2020-06-24 8:55 ` [PATCH v3 09/14] vfio/type1: Support binding guest page tables to PASID Liu Yi L
2020-07-02 21:19 ` Alex Williamson
2020-07-03 6:46 ` Liu, Yi L
2020-06-24 8:55 ` [PATCH v3 10/14] vfio/type1: Allow invalidating first-level/stage IOMMU cache Liu Yi L
2020-07-02 21:19 ` Alex Williamson
2020-07-03 3:47 ` Liu, Yi L
2020-06-24 8:55 ` [PATCH v3 11/14] vfio/type1: Add vSVA support for IOMMU-backed mdevs Liu Yi L
2020-06-24 8:55 ` [PATCH v3 12/14] vfio/pci: Expose PCIe PASID capability to guest Liu Yi L
2020-06-24 8:55 ` [PATCH v3 13/14] vfio: Document dual stage control Liu Yi L
2020-06-29 9:21 ` Stefan Hajnoczi
2020-06-29 9:24 ` Liu, Yi L
2020-06-24 8:55 ` [PATCH v3 14/14] iommu/vt-d: Support reporting nesting capability info Liu Yi L
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