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Subject: [OASIS Issue Tracker] (VIRTIO-154) Document VIRTIO_F_IOMMU_PLATFORM reserved feature bit (33)
[ https://issues.oasis-open.org/browse/VIRTIO-154?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=64259#comment-64259 ] Michael S. Tsirkin commented on VIRTIO-154: ------------------------------------------- Wrong proposal link, ballot withdrawn. > 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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