Messages in this thread | | | Date | Mon, 14 Sep 2009 12:08:55 -0400 | From | Gregory Haskins <> | Subject | Re: [PATCHv5 3/3] vhost_net: a kernel-level virtio server |
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Michael S. Tsirkin wrote: > On Fri, Sep 11, 2009 at 12:00:21PM -0400, Gregory Haskins wrote: >> FWIW: VBUS handles this situation via the "memctx" abstraction. IOW, >> the memory is not assumed to be a userspace address. Rather, it is a >> memctx-specific address, which can be userspace, or any other type >> (including hardware, dma-engine, etc). As long as the memctx knows how >> to translate it, it will work. > > How would permissions be handled?
Same as anything else, really. Read on for details.
> it's easy to allow an app to pass in virtual addresses in its own address space.
Agreed, and this is what I do.
The guest always passes its own physical addresses (using things like __pa() in linux). This address passed is memctx specific, but generally would fall into the category of "virtual-addresses" from the hosts perspective.
For a KVM/AlacrityVM guest example, the addresses are GPAs, accessed internally to the context via a gfn_to_hva conversion (you can see this occuring in the citation links I sent)
For Ira's example, the addresses would represent a physical address on the PCI boards, and would follow any kind of relevant rules for converting a "GPA" to a host accessible address (even if indirectly, via a dma controller).
> But we can't let the guest specify physical addresses.
Agreed. Neither your proposal nor mine operate this way afaict.
HTH
Kind Regards, -Greg
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