Different kernel configuration for different HW ?

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ranshalit
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Different kernel configuration for different HW ?

Post by ranshalit » 2019/11/28 10:12:49

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

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jlehtone
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Re: Different kernel configuration for different HW ?

Post by jlehtone » 2019/11/28 10:55:10

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?

ranshalit
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Re: Different kernel configuration for different HW ?

Post by ranshalit » 2019/11/28 11:19:43

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.

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TrevorH
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Re: Different kernel configuration for different HW ?

Post by TrevorH » 2019/11/28 11:23:56

Rather than posting what you think might be the solution, how about explaining what the actual problem you are trying to solve is?
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ranshalit
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Re: Different kernel configuration for different HW ?

Post by ranshalit » 2019/11/28 12:03:42

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

BShT
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Re: Different kernel configuration for different HW ?

Post by BShT » 2019/11/28 12:20:02

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

ranshalit
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Re: Different kernel configuration for different HW ?

Post by ranshalit » 2019/11/28 12:31:27

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.

BShT
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Re: Different kernel configuration for different HW ?

Post by BShT » 2019/11/28 13:39:42

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

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TrevorH
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Re: Different kernel configuration for different HW ?

Post by TrevorH » 2019/11/28 15:45:03

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.
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