From: Jason Gunthorpe <jgg@nvidia.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>,
"Tian, Kevin" <kevin.tian@intel.com>,
Alex Williamson <alex.williamson@redhat.com>,
Baolu Lu <baolu.lu@linux.intel.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-pci <linux-pci@vger.kernel.org>,
"iommu@lists.linux.dev" <iommu@lists.linux.dev>
Subject: Re: Question about reserved_regions w/ Intel IOMMU
Date: Mon, 19 Jun 2023 11:02:12 -0300 [thread overview]
Message-ID: <ZJBf5DP60prFH5R2@nvidia.com> (raw)
In-Reply-To: <90823b33-1f44-8789-9a38-282407fd9f15@arm.com>
On Mon, Jun 19, 2023 at 11:20:58AM +0100, Robin Murphy wrote:
> On 2023-06-16 19:59, Jason Gunthorpe wrote:
> > On Fri, Jun 16, 2023 at 05:34:53PM +0100, Robin Murphy wrote:
> > >
> > > If the system has working ACS configured correctly, then this issue should
> > > be moot;
> >
> > Yes
> >
> > > if it doesn't, then a VFIO user is going to get a whole group of
> > > peer devices if they're getting anything at all, so it doesn't seem entirely
> > > unreasonable to leave it up to them to check that all those devices'
> > > resources play well with their expected memory map.
> >
> > I think the kernel should be helping here.. 'go figure it out from
> > lspci' is a very convoluted and obscure uAPI, and I don't see things
> > like DPDK actually doing that.
> >
> > IMHO the uAPI expectation is that the kernel informs userspace what
> > the usable IOVA is, if bridge windows and lack of ACS are rendering
> > address space unusable then VFIO/iommufd should return it as excluded
> > as well.
> >
> > If we are going to do that then all UNAMANGED domain users should
> > follow the same logic.
> >
> > We probably have avoided bug reports because of how rare it would be
> > to see a switch and an UNMANAGED domain using scenario together -
> > especially with ACS turned off.
> >
> > So it is really narrow niche.. Obscure enough I'm not going to make
> > patches :)
>
> The main thing is that we've already been round this once before; we tried
> it 6 years ago and then reverted it a year later for causing more problems
> than it solved:
As I said earlier in this thread if we do it for VFIO then the
calculation must be precise and consider bus details like
ACS/etc. eg VFIO on an ACS system should not report any new regions.
It looks like that thread confirms we can't create reserved regions
which are wrong :)
I think Alex is saying the same things I'm saying in that thread too:
https://lore.kernel.org/all/20180226161310.061ce3a8@w520.home/
(b) is what the kernel should help prevent.
And it is clear there are today scenarios where a VFIO user will get
data loss because the reported valid IOVA from the kernel is
incorrect. Fixing this is hard, much harder than what commit
273df9635385 ("iommu/dma: Make PCI window reservation generic") has.
Thanks,
Jason
next prev parent reply other threads:[~2023-06-19 14:02 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAKgT0UezciLjHacOx372+v8MZkDf22D5Thn82n-07xxKy_0FTQ@mail.gmail.com>
2023-06-07 23:03 ` Question about reserved_regions w/ Intel IOMMU Alexander Duyck
2023-06-08 3:03 ` Baolu Lu
2023-06-08 14:33 ` Alexander Duyck
2023-06-08 15:38 ` Ashok Raj
2023-06-08 17:10 ` Alexander Duyck
2023-06-08 17:52 ` Ashok Raj
2023-06-08 18:15 ` Alexander Duyck
2023-06-08 18:02 ` Robin Murphy
2023-06-08 18:17 ` Alexander Duyck
2023-06-08 15:28 ` Robin Murphy
2023-06-13 15:54 ` Jason Gunthorpe
2023-06-16 8:39 ` Tian, Kevin
2023-06-16 12:20 ` Jason Gunthorpe
2023-06-16 15:27 ` Alexander Duyck
2023-06-16 16:34 ` Robin Murphy
2023-06-16 18:59 ` Jason Gunthorpe
2023-06-19 10:20 ` Robin Murphy
2023-06-19 14:02 ` Jason Gunthorpe [this message]
2023-06-20 14:57 ` Alexander Duyck
2023-06-20 16:55 ` Jason Gunthorpe
2023-06-20 17:47 ` Alexander Duyck
2023-06-21 11:30 ` Robin Murphy
2023-06-16 18:48 ` Jason Gunthorpe
2023-06-21 8:16 ` Tian, Kevin
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