intel iommu pasid question

intel iommu pasid question

[周光迪]

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Hi all，  


I am currently developing a pcie device driver on Linux kernel 4.4 or later. I want to use pasid to directly access user-mode memory. But I found that the iommu of my development machine does not support pasid.pasid_enabled(iommu) or pasid_supported(iommu) return false.


I want to know how to enable the pasid function of intel iommu，Is there a separate switch to enable the iommu pasid function or the iommu hardware implementation has decided whether to support PASID and the software cannot configure it？


How can I check which version of intel vt-d is implemented by iommu on my platform?Does the value of iommu's Version Register represent the vt-d version? 
the iommu version register of my intel xeon gold 5118 platform server is 1.0










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intel iommu pasid question

[周光迪]

Hi all，  


I am currently developing a pcie device driver on Linux kernel 4.4 or later. I want to use pasid to directly access user-mode memory. But I found that the iommu of my development machine does not support pasid.pasid_enabled(iommu) or pasid_supported(iommu) return false.


I want to know how to enable the pasid function of intel iommu，Is there a separate switch to enable the iommu pasid function or the iommu hardware implementation has decided whether to support PASID and the software cannot configure it？


How can I check which version of intel vt-d is implemented by iommu on my platform?Does the value of iommu's Version Register represent the vt-d version? 
the iommu version register of my intel xeon gold 5118 platform server is 1.0


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RE: intel iommu pasid question

[Liu, Yi L]

> From: iommu [mailto:iommu-bounces@lists.linux-foundation.org] On Behalf Of ???
> Sent: Saturday, January 18, 2020 12:21 PM
> To: iommu@lists.linux-foundation.org
> Subject: intel iommu pasid question
> 
> Hi all，
> 
> 
> I am currently developing a pcie device driver on Linux kernel 4.4 or later. I want to
> use pasid to directly access user-mode memory. But I found that the iommu of my
> development machine does not support pasid.pasid_enabled(iommu) or
> pasid_supported(iommu) return false.

Echo Baolu's comment.

> 
> I want to know how to enable the pasid function of intel iommu，Is there a separate
> switch to enable the iommu pasid function or the iommu hardware implementation
> has decided whether to support PASID and the software cannot configure it？

You can check if VT-d is enabled in Linux kernel by below command:

dmesg | grep “Intel(R) Virtualization Technology for Directed I/O”

> 
> How can I check which version of intel vt-d is implemented by iommu on my
> platform?Does the value of iommu's Version Register represent the vt-d version?
> the iommu version register of my intel xeon gold 5118 platform server is 1.0

You can check VT-d PASID support by echo "dmesg | grep “dmar”"

You should get some info like below. Check PASID support by checking bit 40 of ecap register.
[    0.078285] DMAR: dmar1: reg_base_addr fed90000 ver 1:0 cap 1c0000c40660462 ecap 7e3ff0505e
[    0.078289] DMAR: dmar2: reg_base_addr fed91000 ver 1:0 cap d2008c40660462 ecap f050da

Also, if your kernel supports iommu debugfs, you may dump the translation.
structures in /sys/kernel/debug/iommu/intel/dmar_translation_struct. There
is a bit is Context Entry which enables PASID. (bit 3 of Context entry).

Regards,
Yi Liu

> 
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Re: intel iommu pasid question

[Lu Baolu]

Hi Guangdi,

On 1/18/20 12:18 PM, 周光迪 wrote:
> Hi all，
> 
> 
> I am currently developing a pcie device driver on Linux kernel 4.4 or
> later. I want to use pasid to directly access user-mode memory. But I
> found that the iommu of my development machine does not support 
> pasid.pasid_enabled(iommu) or pasid_supported(iommu) return false.

Intel IOMMU driver currently supports SVA through APIs defined in
include/linux/intel-svm.h. We are switching to use the APIs defined
in driver/iommu/iommu.c, but it should last for some while.

Best regards,
baolu
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