Re: rfc: vhost user enhancements for vm2vm communication

On 2015-09-03 10:37, Michael S. Tsirkin wrote:

On Thu, Sep 03, 2015 at 10:21:28AM +0200, Jan Kiszka wrote:

quoted

On 2015-09-03 10:08, Michael S. Tsirkin wrote:

quoted

IOW if you wish, you actually can create a shared memory device,
make it accessible to the IOMMU and place some or all
data there.

Actually, that could also be something more sophisticated, including
virtio-net, IF that device will be able to express its DMA window
restrictions (a bit like 32-bit PCI devices being restricted to <4G
addresses or ISA devices <1M).

Jan

Actually, it's the bus restriction, not the device restriction.

So if you want to use bounce buffers in the name of security or
real-time requirements, you should be able to do this if virtio uses the
DMA API.

Bounce buffer will only be the simplest option (though fine for low-rate
traffic that we also have in mind, like virtual consoles). Given
properly-sized regions, even if fixed, and the right communication
stacks, you can directly allocate application buffers in those regions
and avoid most to all copying.

In any case, if we manage to address this variation along with your
proposal, that would help tremendously.

Jan

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