Re: [PATCH net-next] xsk: introduce xsk_dma_ops

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


On Wed, Apr 19, 2023 at 09:45:06AM -0700, Jakub Kicinski wrote:
> > Can you explain what the actual use case is?
> > 
> > From the original patchset I suspect it is dma mapping something very
> > long term and then maybe doing syncs on it as needed?
> In this case yes, pinned user memory, it gets sliced up into MTU sized
> chunks, fed into an Rx queue of a device, and user can see packets
> without any copies.

How long is the life time of these mappings?  Because dma_map_*
assumes a temporary mapping and not one that is pinned bascically

> Quite similar use case #2 is upcoming io_uring / "direct placement"
> patches (former from Meta, latter for Google) which will try to receive
> just the TCP data into pinned user memory.

I don't think we can just long term pin user memory here.  E.g. for
confidential computing cases we can't even ever do DMA straight to
userspace.  I had that conversation with Meta's block folks who
want to do something similar with io_uring and the only option is an
an allocator for memory that is known DMAable, e.g. through dma-bufs.

You guys really all need to get together and come up with a scheme
that actually works instead of piling these hacks over hacks.
Virtualization mailing list

[Index of Archives]     [KVM Development]     [Libvirt Development]     [Libvirt Users]     [CentOS Virtualization]     [Netdev]     [Ethernet Bridging]     [Linux Wireless]     [Kernel Newbies]     [Security]     [Linux for Hams]     [Netfilter]     [Bugtraq]     [Yosemite Forum]     [MIPS Linux]     [ARM Linux]     [Linux RAID]     [Linux Admin]     [Samba]

  Powered by Linux