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PCI_MSI_2 skips MSI-only endpoints in Linux vector uniqueness test

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
72/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
c, linux
Domain
operating-systems, testing-qa

Research direction

Start with the Linux ACS implementation for the PCI_MSI_2 vector uniqueness test and trace its MSI/MSI-X capability check into the Linux PAL vector read path. Verify the test includes endpoints supporting either capability, handles both vector sources, and skips only devices supporting neither MSI nor MSI-X.

Written by the indexing model from the issue text.

Description

The PCI_MSI_2 rule applies to MSI(-X), so endpoints that support MSI only should be valid targets for the test.
In the current Linux ACS implementation, the vector uniqueness test appears to skip MSI-only endpoints because the capability check requires both MSI-X and MSI capability discovery to pass before the device is considered.
Current behavior:

  • Endpoint supports MSI only.
  • Endpoint does not support MSI-X.
  • PCI_MSI_2 skips the device.
  • Test may report no MSI vectors found / skip, even though an MSI-capable endpoint is present.
    Expected behavior:
  • PCI_MSI_2 should accept endpoints that support either MSI or MSI-X.
  • MSI-only endpoints should be included in the vector uniqueness validation.
  • The test should skip only devices that support neither MSI nor MSI-X.
    Suggested fix:
  • Update the capability check so the device is skipped only when both MSI-X and MSI capabilities are absent.
  • Ensure the Linux PAL vector read path continues to handle both MSI-X table entries and MSI capability registers.
    Impact:
  • MSI-only platforms cannot currently obtain automated ACS coverage for PCI_MSI_2.
  • Such platforms may need manual validation until this is fixed.
Dominant language
C
Stars
23
Forks
39
Avg merge
6h 54m
Merged PRs (30d)
90

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