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riscv-non-isa / riscv-iommu

RISC-V IOMMU Specification
https://jira.riscv.org/browse/RVG-55
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How does the IO-bridge handle ATS translation requests when the address is a virtual interrupt file address? #268

Closed 18772820305 closed 11 months ago

18772820305 commented 11 months ago

If an ATS translation request, after being translated by the IOMMU, finds that the requested address A is a virtual interrupt file address, and upon obtaining the MSIPTE, it is determined to be a PTE in MRIF mode. Then, the IOMMU will return information such as is_msi/is_mrif/mrif_nid/mrif_addr to the IO-bridge. How will the IO-bridge handle these contents after retrieval?

ved-rivos commented 11 months ago

Please see the handling specified in section 2.6.

If the translation request has an address determined to be an MSI address but the MSI PTE is configured in MRIF mode then a Success response is generated with R, W, and U bit set to 1. The U bit being set to 1 in the response instructs the device that it must only use Untranslated requests to access the implied 4 KiB memory range.

When a MSI PTE is configured in MRIF mode, a MSI write with data value D requires the IOMMU to set the interrupt-pending bit for interrupt identity D in the MRIF. A translation request from a device to a GPA that is mapped through a MRIF mode MSI PTE is not eligible to receive a translated address. This is accomplished by setting "Untranslated Access Only" (U) field of the returned response to 1.

18772820305 commented 11 months ago

If the translation request has an address determined to be an MSI address ，and the MSI PTE is configured in MRIF mode then a Success response is generated by IO-bridge. Is it useful for the IOMMU to return NID and NPPN to the IO-bridge?

ved-rivos commented 11 months ago

Is it useful for the IOMMU to return NID and NPPN to the IO-bridge?

The contents of the MSI PTE are not useful as they are not included in the response to the device.

ved-rivos commented 11 months ago

I hope that addressed the question @18772820305. Closing this issue. Please feel free to ask if there are further questions.