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Subject: Re: Re: [virtio-comment] About adding a new device type virtio-nvme
On Tue, Jan 17, 2023 at 05:41:57PM +0800, äèä wrote:
> On Tue, 17 Jan 2023 09:32:05 +0100ïDavid wroteï
> >On 17.01.23 03:04, äèä wrote:
>
>
>
> >> virtio-nvmeÂadvantages :
> >> 1)Â live migration
> >> 2)Â support remote storage
>
>
>
> >At least 1) is an implementation detail in the NVME implementation in
> >the hypervisor. I suspect 2) in a similar way, or is there a fundamental
> >issue with that?
>
>
>
> >One problematic thing about the NVME implementation in QEMU is that it
> >will pin (via vfio) all guest RAM. Could that be avoided using
> >virtio-NVME, or what exactly would be the difference between virtio-nvme
> >and ordinary NVME?
>
>
>
> In the virtualization scenario where devices are offload to hardwareï
>
>
> NVMEï
> ---------------------------------------------------------------------------------------------------------------------
> _____________________________________________________________________________
> | ___________________________________________________________ |
> | | _____________________________________________________ | |
> | | | | | |
> | | | __________________________________ | | |
> | | | | ______ | | | | ______
> | | | User | | Mem |-----------------------|----|-|----|-----> | |
> | | | | |______| SPDK | | | | (gVA) |______|
> | | | | (gVA) | | | | | |
> | | | |______|___________________________| | | | | |
> | | |--GuestOS----------|--------------------------------| | | | |
> | | | ______\/__________________________ | | | | |
> | | VM | | VFIO | | | | | |
> | User | | Kernel |___________ __________________| | | | | |
> | | | | vfio-pci | | | | | | | |
> | | | | (gIOVA) | | vfio_iommu_type1 | | | | | |
> Software | | | |______|____|___|__________________| | | | | |
> | | |___________________|________________________________| | | | |
> | | ___________________|________________________________ | | | |
> | | | ______|____ __________________ | | | \/ \/
> | | | | \/ | | | | | | ______
> | | | | NVME | | vIOMMU | | | | | |
> | | | QEMU | Instance | | --|----|-|----|-----> |______|
> | | | | (gIOVA) | | (gIOVA-->gPA) | | | | (gPA) | |
> | | | |_____|_____| |__________________| | | | | |
> | | |__________________|_________________________________| | | | |
> | |_______________________|___________________________________| | | |
> |---HostOS---------------------------|----------------------------------------| | |
> | _______________________|___________________________________ | | |
> | | | | | | |
> | | | VFIO | | | |
> | Kernel |_______________________|_____ _________________________| | | |
> | | \/ | | | | | |
> | | vfio-pci | | vfio_iommu_type1 | | | |
> | | | | | | | | |
> | |_______________________|_____|___|_________________________| | | |
> |____________________________________|________________________________________| | |
> -----------------------------------------------|-------------------------------------------------|----|--------------
> ____________________________________\/____ _________________________ ___\/___\/___________
> | | | | | | | | | |
> Hardware | | | DMA (gIOVA) --|---|-> IOMMU --|---------|->|______| |
> | | |_____________________________| | (gIOVA-->hPA) | (hPA) | Physical Memory |
> | DPU | | |_________________________| |_____________________|
> | | NVME-of |
> | |__________________________________|
> | | |
> |___________________________|______________|
> --------------------------------------|------------------------------------------------------------------------------
> | TCP (RDMA, and so on)
> ______________v__________
> | |
> Remote storage | |
> | Network Storage |
> | |
> |_________________________|
>
> ---------------------------------------------------------------------------------------------------------------------
>
>
> It is difficult to implement PCIe passthrough live migration.
Linux commit 115dcec65f61d53e25e1bed5e380468b30f98b14 ("vfio: Define
device migration protocol v2") defines the VFIO migration API and it's
implemented by several drivers in the kernel.
Can you explain the difficulty of implementing PCIe passthrough live
migration in more detail?
>
>
>
> Â
> virtio-nvme:
> ---------------------------------------------------------------------------------------------------------------------
> _____________________________________________________________________________
> | ___________________________________________________________ |
> | | _____________________________________________________ | |
> | | | | | |
> | | | __________________________________ | | |
> | | | | ______ | | | | ______
> | | | User | | Mem |-----------------------|----|-|----|-----> | |
> | | | | |______| SPDK | | | | (gVA) |______|
> | | | | (gVA) | | | | | |
> | | | |______|___________________________| | | | | |
> | | |--GuestOS----------|--------------------------------| | | | |
> | | | ______v___________________________ | | | | |
> | | VM | | VFIO | | | | | |
> | User | | Kernel |___________ __________________| | | | | |
> | | | | vfio-pci | | | | | | | |
> | | | | (gIOVA) | | vfio_iommu_type1 | | | | | |
> Software | | | |______|____|___|__________________| | | | | |
> | | |___________________|________________________________| | | | |
> | | ___________________|________________________________ | | | |
> | | | ______v____ __________________ | | | v v
> | | | |virtio-NVME| | | | | | ______
> | | | | Instance | | vIOMMU | | | | | |
> | | | QEMU | | | --|----|-|----|-----> |______|
> | | | | vhost-vdpa| | (gIOVA-->gPA) | | | | (gPA) | |
> | | | |__(gIOVA)__| |__________________| | | | | |
> | | |__________________|_________________________________| | | | |
> | |_______________________|___________________________________| | | |
> |---HostOS---------------------------|----------------------------------------| | |
> | _______________________|___________________________________ | | |
> | | | | | | |
> | | | vDPA | | | |
> | Kernel |_______________________v_____ _________________________| | | |
> | | | | | | | | |
> | | vdpa-device | | | | | | |
> | | (Virtual device) | | | | | | |
> | |_______________________|_____|___|_________________________| | | |
> |____________________________________|________________________________________| | |
> -----------------------------------------------|-------------------------------------------------|----|--------------
> ____________________________________v_____ _________________________ ___v____v____________
> | | | | | | | | | |
> Hardware | | | DMA (gIOVA) --|---|-> IOMMU --|---------|->|______| |
> | | |_____________________________| | (gIOVA-->hPA) | (hPA) | Physical Memory |
> | DPU | | |_________________________| |_____________________|
> | | virtio-nvme-of |
> | |__________________________________|
> | | |
> |___________________________|______________|
> --------------------------------------|------------------------------------------------------------------------------
> | TCP (RDMA, and so on)
> ______________v__________
> | |
> Remote storage | |
> | Network Storage |
> | |
> |_________________________|
>
> ---------------------------------------------------------------------------------------------------------------------
> Based on the vDPA framework, it supports live migration.
The two diagrams are quite similar. Did you want to highlight a
difference between the two approaches in the diagram?
Stefan
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