[dpdk-dev] [EXT] Re: [PATCH v4 0/4] Fixes on IOVA mode selection

[Jerin Jacob Kollanukkaran]

> -----Original Message-----
> From: Burakov, Anatoly <anatoly.burakov at intel.com>
> Sent: Tuesday, July 23, 2019 7:27 PM
> To: Thomas Monjalon <thomas at monjalon.net>
> Cc: Jerin Jacob Kollanukkaran <jerinj at marvell.com>; Stojaczyk, Dariusz
> <dariusz.stojaczyk at intel.com>; David Marchand
> <david.marchand at redhat.com>; dev at dpdk.org
> Subject: [EXT] Re: [dpdk-dev] [PATCH v4 0/4] Fixes on IOVA mode selection
> 
> ----------------------------------------------------------------------
> 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-
> sysfs.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?

I checked with a x86 and arm64 machine. I could not see "/sys/devices/virtual/iommu"
But looks like "/sys/class/iommu/" present when iommu present.

$ uname -a
Linux jerin-lab 5.1.15-arch1-1-ARCH #1 SMP PREEMPT Tue Jun 25 04:49:39 UTC 2019 x86_64 GNU/Linux

$ ls /sys/devices/virtual/
bdi  dmi  drm  graphics  mem  misc  msr  net  powercap  thermal  tty  vc  vtconsole  workqueue

# ls /sys/class/iommu/

# uname -a                                                      
Linux alarm 4.14.76-5.0.0-g12f0519 #63 SMP PREEMPT Thu Jul 11 17:43:54 IST 2019 aarch64 GNU/Linux 

# ls /sys/devices/virtual/
bdi  block  graphics  input  mem  misc  net  otx-bphy-ctr  otx-gpio-ctr  ppp  tty  vc  vfio  vtconsole  workqueue

# ls /sys/class/iommu/
smmu3.0x0000830000000000

> 
> --
> Thanks,
> Anatoly