Scalable Mode Translation for DMA Remapping in Xeon Processors

[gkgabel]

I wanted to ask if there is a specific CPU family from which Scalable translation mode for DMA features are enabled. I am looking to buy a processor for our lab and want these features as described in Intel's Virtualization Directed I/O Spec. I am basically looking for access flag support in either legacy mode or scalable mode via these flags. 

- SSADE: Second Stage Access/Dirty bit Enable

- SMTS: Scalable Mode Translation Support

I checked these flags via extended capability register exposed in Linux kernels via sysfs path (/sys/class/iommu/dmar0/intel-iommu/ecap) and am not able to find these bits set in many systems. I will list these values for other processors that we have in our lab.

1. Intel Xeon Silver 4314 Processor: ecap: 60000f050df  SSADE: unset SMTS: unset
2. Intel Xeon Platinum 8360Y Processor:  ecap: 60000f050df  SSADE: unset SMTS: unset
3. Intel Xeon Silver 4114 Processor: ecap: f020de  SSADE: unset SMTS: unset
4. Intel Xeon Processor E5-2640 v4: ecap: f020de  SSADE: unset SMTS: unset
5. Intel Xeon Gold 5512U Processor: ecap: 3ef9e86f050df  SSADE: set SMTS: set
6. Intel Xeon Platinum 8462Y+: ecap: 3ee9e86f050df SSADE: set SMTS: set

I want to ask if there is a CPU family that I should be targeting that has these features enabled. Also, can they be tweaked from the BIOS? These are HW registers, so I suppose they are not affected by kernel config. I see that in the 5,6 where these features are enabled, they are fairly newer compared to others. So, are these available in newer families, or is there some other dependency that I might be overlooking? 

Also how to check if I am runnng in legacy translation mode, one way is via register read for field RTADDR_REG.ttm. But is there a way to read it via sysfs. I want to check if it runs in legacy mode then if it supports access bits. Please correct me if I have been wrong anywhere and please let me know if I am missing something.

[ManoranjanDas]

Hello gkgabel,  

Greetings from Intel!  

We have noted your report and are currently reviewing the case. Rest assured, we will thoroughly investigate the matter and get back to you as soon as possible. 

Please feel free to reply to this email. We're here to assist you every step of the way.  

Regards,  

Manoranjan  

Intel Customer Support Technician  

[Azhari_Intel]

Hello gkgabel,

Good day to you!

Regarding to your enquiries, kindly refer below.

1. The following processors show these features/bits are set. Is this because these are from newer processor families? Is it missing another dependency?

• Intel Xeon Gold 5512U Processor: ecap: 3ef9e86f050df, SSADE: set, SMTS: set
• Intel Xeon Platinum 8462Y+: ecap: 3ee9e86f050df, SSADE: set, SMTS: set

Answer: These are newer processors from the 5th Gen (5512U) and 4th Gen (8462Y+) families, previous generations did not support these capabilities. You can see more details below, but an NDA is required to access. Please check if you have a valid CNDA number with Intel.

Please find the confidential document numbers below. If you have access to RDC, you can locate it there. Else, if you do not have access, please refer on the link: https://www.intel.com/content/www/us/en/support/articles/000058073/programs/resource-and-documentation-center.html

a) Doc 723370

b) Doc 612246

c) Doc 737845

d) Doc 637776

2. Are the features above supported in Legacy Mode Translation

Answer: No, these are only supported in Scalable Mode Translation

3. How to check if it is running in legacy mode translation, one way is via register read for field RTADDR_REG.ttm. But is there a way to read it via sysfs?

Answer: Reading the registers is the optimal way to confirm this

Let us know if you have further concerns.

Regards,

Azhari_Intel

[IntelSupport]

Hello Gkgabel,

Good day!

I’m reaching out to follow up on our previous communication. I hope the information we provided was helpful.

Could you please confirm if everything has been resolved to your satisfaction? Please let us know, If you need any additional details or further assistance.

Thank you and best regards,

Shankith K P

Intel Customer Support Technician

[gkgabel]

Hello,

Many thanks for the answer. It resolves my queries. I however have issues with accessing the documents mentioned above from RDC as we don't have CNDA access as of now. Are there any other documents available in public domain for these?

Thanks

[IntelSupport]

Hello Gkgabel,

Thank you for getting back to us.

We’re glad to hear that the information provided was helpful.

Regarding access to the document, please note that certain information is classified as Intel Confidential and is not publicly accessible without an active CNDA (Corporate Non-Disclosure Agreement) with Intel.

For more details, kindly refer to the article linked below:

https://www.intel.com/content/www/us/en/support/articles/000058073/programs/resource-and-documentation-center.html

Thanks and regards,

Shankith K P

Intel Customer Support Technician

[IntelSupport]

Hello gkgabel,

Greetings from Intel!

We wanted to check in and confirm whether all your queries have been resolved. May we proceed with closing this case?

If you need any further assistance, please don’t hesitate to reach out. We're here to help!

Regards,   

Shankith K P    

Intel Customer Support Technician  

[gkgabel]

I appreciate the swift response. I had a follow up on the a previous response to my question. Are there any Intel desktop processors where these capabilities are set and hence the IOMMU access bits are supported?

Thanks,

Gulshan

[Sachinks]

Hello gkgabel,

Good day!

Thank you for your reply. Regarding your query related to desktop processors, we will check this from our end and get back to you with an update at the earliest.

Regards,

Sachin KS

Intel Customer Support Technician

[ArchieD_Intel]

Hi gkgabel,

Intel desktop processors that support Intel Virtualization Technology for Directed I/O (VT-d) have the IOMMU (Input-Output Memory Management Unit) capabilities. VT-d is a feature that allows for better control and isolation of I/O devices in virtualized environments, and it is supported on many Intel processors, particularly those aimed at higher-end desktops and workstations.

You may check Intel® Product Specifications for the list of processors that supports this feature.

If you have any questions, please let us know. Thank you.

Best regards,

Archie D.

Intel Customer Support Technician

[gkgabel]

Thanks, but in my original question, I mentioned that though all the processors that I specified supported VT-d, the access bit support, either in scalable mode or second-level translation in legacy mode, was only present in a few processors. So, which series among desktop processors that support VT-d has these features?

Thanks,

Gulshan

[ArchieD_Intel]

Hi gkgabel,

For desktop processors, the Intel Xeon W series is most likely to support IOMMU access bits in scalable mode or second-level translation in legacy mode. These processors are designed for workstations and offer advanced virtualization features, including VT-d. Additionally, other high-end Intel Core i9 processors may also support these capabilities, but the Xeon W series is generally the best choice for comprehensive IOMMU support in desktop environments.

You may also check Intel® Product Specification Comparison for the newer processors that supports this.

If you have any questions, please let us know. Thank you.

Best regards,

Archie D.

Intel Customer Support Technician

[ArchieD_Intel]

Hi gkgabel,

Did you have a chance to review the previous post? Please feel free to reach out if you have any questions. Thank you.

Best regards,

Archie D.

Intel Customer Support Technician

[ArchieD_Intel]

Hi gkgabel,

I have not heard back from you so I will close this inquiry now. If you need further assistance, please submit a new question as this thread will no longer be monitored.

Best regards,

Archie D.

Intel Customer Support Technician