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

[Burakov, Anatoly]

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?

-- 
Thanks,
Anatoly