CentOS

Hello,

When installing centos8 on x86 computer, does it detect the cpu first, and then install specific configuration according to cpu ?
I ask because we observe different behavior between 2 computers, with PCIe.
In one of them, the PCIe device manage to access RAM (using DMA), but in the other one it fails.

I suspect that maybe one of them disables iommu and the other one enables it. Does it make sense that installation decides to enable/disable iommu according to architecture ?

Thanks,
ranran

No.

AFAIK, iommu has to be explicitly enabled with kernel parameter and installer does not do that for you.

Are your hardware's identical, including the firmware settings?

I tried to add iommu=pt but it does not help
I also wander why in the 1st computer I did not need to add this, and all works fine.

Rather than posting what you think might be the solution, how about explaining what the actual problem you are trying to solve is?

Hi,

The problem is:
I have a simple kernel module which allocates continuous physical memory (using dma_alloc_coherent) and provide it to PCIe connected FPGA device for DMA access, 64-bit addressing PCIe.
But when FPGA tries to access the cpu RAM (using FPGA's dma), it can't access and fails. This is with a lenovo computer ( Intel(R) Xeon(R) CPU E5-2603 0 @ 1.80GHz)

In first step, I suspected kernel 4.18, but installing the same OS (centos 8), same kernel module, and same FPGA in older chip computer (Intel(R) Core(TM)2 Duo CPU U7500 @ 1.06GHz ) - it all works perfectly.

I started suspecting the lenovo machine, but installing windows on same machine, I get that FPGA can do DMA without any issues.

Thank you

look if you have the same BIOS version and settings, look at other firmware too

Right, I suspected BIOS, but on installing windows on the problematic machine (Intel DUI) , it all works well.
It means that with the same BIOS, it works.

you can´t compare linux and windows behavior

IOMMU seems to have some UEFI dependence and UEFI is not windows nor linux...

try to update your BIOS

Also while not directly answering the questions, https://lists.linuxfoundation.org/piper ... 12168.html has some useful info if you read the entire thread. On Intel it says that you need to enable VT-d to use that.