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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