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Explained below in the design section and also in relevant patches 6 to 11. >> It has its own small Device ID range. It does not have I/O >> region BAR; instead it exposes legacy configuration and device >> specific registers at an offset in the memory region BAR. >> >> Such transitional MMR devices will be used at the scale of >> thousands of devices using PCI SR-IOV and/or future scalable >> virtualization technology to provide backward >> compatibility (for legacy devices) and also future >> compatibility with new features. >> >> Usecase: >> -------- >> 1. A hypervisor/system needs to provide transitional >> virtio devices to the guest VM at scale of thousands, >> typically, one to eight devices per VM. >> >> 2. A hypervisor/system needs to provide such devices using a >> vendor agnostic driver in the hypervisor system. > > Is the idea that the hypervisor configures the new Transitional MMR > devices and makes them appear like virtio-pci Transitional devices? > Yes, but hypervisor is not involved in any configuration parsing or anything of that nature. It is only a passthrough fowarder from emulated IOBAR to memory mapped legacy registers. In other words, hypervisor do not care for the registers content at all. > In other words, the guest doesn't know about Transitional MMR and does > not need any code changes. > >> 3. A hypervisor system prefers to have single stack regardless of >> virtio device type (net/blk) and be future compatible with a >> single vfio stack using SR-IOV or other scalable device >> virtualization technology to map PCI devices to the guest VM. >> (as transitional or otherwise) > > What does this paragraph mean? > It means regardless of a VF being transitional MMR VF or 1.x VF without any MMR extensions, there is single vfio virtio driver handling both type of devices to map to the guest VM. > > Modern devices were added to Linux in 2014 and support SR-IOV. > Why is it > important to support Transitional (which really means Legacy devices, > otherwise Modern devices would be sufficient)? > To support guest VMs which only understand legacy devices and unfortunately they are still in much wider use by the users. --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from ws5-mx01.kavi.com (ws5-mx01.kavi.com [34.193.7.191]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DFA0FC761AF for ; 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Explained below in the design section and also in relevant patches 6 to 11. >> It has its own small Device ID range. It does not have I/O >> region BAR; instead it exposes legacy configuration and device >> specific registers at an offset in the memory region BAR. >> >> Such transitional MMR devices will be used at the scale of >> thousands of devices using PCI SR-IOV and/or future scalable >> virtualization technology to provide backward >> compatibility (for legacy devices) and also future >> compatibility with new features. >> >> Usecase: >> -------- >> 1. A hypervisor/system needs to provide transitional >> virtio devices to the guest VM at scale of thousands, >> typically, one to eight devices per VM. >> >> 2. A hypervisor/system needs to provide such devices using a >> vendor agnostic driver in the hypervisor system. > > Is the idea that the hypervisor configures the new Transitional MMR > devices and makes them appear like virtio-pci Transitional devices? > Yes, but hypervisor is not involved in any configuration parsing or anything of that nature. It is only a passthrough fowarder from emulated IOBAR to memory mapped legacy registers. In other words, hypervisor do not care for the registers content at all. > In other words, the guest doesn't know about Transitional MMR and does > not need any code changes. > >> 3. A hypervisor system prefers to have single stack regardless of >> virtio device type (net/blk) and be future compatible with a >> single vfio stack using SR-IOV or other scalable device >> virtualization technology to map PCI devices to the guest VM. >> (as transitional or otherwise) > > What does this paragraph mean? > It means regardless of a VF being transitional MMR VF or 1.x VF without any MMR extensions, there is single vfio virtio driver handling both type of devices to map to the guest VM. > > Modern devices were added to Linux in 2014 and support SR-IOV. > Why is it > important to support Transitional (which really means Legacy devices, > otherwise Modern devices would be sufficient)? > To support guest VMs which only understand legacy devices and unfortunately they are still in much wider use by the users. This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/