On 23-Jul-19 3:36 PM, Jerin Jacob Kollanukkaran wrote:
-----Original Message-----
From: Burakov, Anatoly <anatoly.bura...@intel.com>
Sent: Tuesday, July 23, 2019 8:00 PM
To: Thomas Monjalon <tho...@monjalon.net>
Cc: Jerin Jacob Kollanukkaran <jer...@marvell.com>; Stojaczyk, Dariusz
<dariusz.stojac...@intel.com>; David Marchand
<david.march...@redhat.com>; dev@dpdk.org
Subject: [EXT] Re: [dpdk-dev] [PATCH v4 0/4] Fixes on IOVA mode selection
On 23-Jul-19 2:56 PM, Burakov, Anatoly wrote:
On 23-Jul-19 11:25 AM, Thomas Monjalon wrote:
23/07/2019 11:57, Burakov, Anatoly:
A machine without an IOMMU shouldn't have picked IOVA as VA in the
first place. Perhaps this is something we could fix? I'm not sure
how to detected that condition though, i don't think there's a
mechanism to know that for sure. Some kernels create a "iommu" sysfs
directories, but i'm not too sure if they're 1) there for older
kernels we support, and
2) always there.
[..]
On my machine, "/sys/devices/virtual/iommu" exists when IOMMU is
enabled, but doesn't exist if it isn't ("/sys/class/iommu" exists in
both cases, but is empty when IOMMU is disabled). Perhaps we could
go off that?
Yes, good idea.
We need to check how these sysfs entries are managed, and how old
they are by looking at Linux code history.
Quick (and by no means thorough) Google reveals that IOMMU driver's
sysfs-related code dates back as far as kernel version 3.17:
https://elixir.bootlin.com/linux/v3.17.8/source/drivers/iommu/iommu-sy
sfs.c
I'm not a kernel code expert, but the code *looks* like it's creating
an IOMMU-related entry in sysfs. So, i take it we can be reasonably
sure of these entries' presence at least since v3.17 onwards? Do we
support kernels which don't have this code?
After a short chat with Ferruh, i think we have even better way to determine
whether IOMMU is enabled - the /sys/kernel/iommu filesystem.
Those are created whenever it is possible for VFIO to run, even if VFIO driver
itself is not loaded. These have been there since kernel 3.6, so our minimum
requirements are met with this approach, i believe.
I can see /sys/kernel/iommu_groups/ on IOMMU systems not /sys/kernel/iommu
Sorry, yes, a typo. It's /sys/kernel/iommu_groups/.
--
Thanks,
Anatoly
--
Thanks,
Anatoly
