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Subject: [OASIS Issue Tracker] (VIRTIO-154) Document VIRTIO_F_IOMMU_PLATFORM reserved feature bit (33)
Michael S. Tsirkin created VIRTIO-154: ----------------------------------------- Summary: Document VIRTIO_F_IOMMU_PLATFORM reserved feature bit (33) Key: VIRTIO-154 URL: https://issues.oasis-open.org/browse/VIRTIO-154 Project: OASIS Virtual I/O Device (VIRTIO) TC Issue Type: Bug Affects Versions: virtio 1.0 cs04 Environment: Reported-by: Will Deacon <will.deacon@arm.com> Reporter: Michael S. Tsirkin Assignee: Michael S. Tsirkin Fix For: virtio 1.1 cs01 On most virtio systems, physical addresses are provided from the driver to the device and subsequently used to access memory directly. However, some systems feature an IOMMU that complicates things slightly: - The IOMMU might require configuration for DMA to work at all. Once configured, the driver must pass bus addresses to the device, which are then translated by the IOMMU into physical addresses in memory. - The IOMMU might be bypassed by virtio DMA. In this case, physical addresses must still be provided to the device by the driver, even though an IOMMU appears to be present. This has been solved by the addition of a new reserved feature bit, VIRTIO_F_IOMMU_PLATFORM, to describe the two cases above. Legacy systems will not negotiate the feature, and therefore continue to operate directly on physical addresses. -- This message was sent by Atlassian JIRA (v6.2.2#6258)
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