On Fri, May 29, 2015 at 06:44:56PM +1000, Alexey Kardashevskiy wrote: > We are adding support for DMA memory pre-registration to be used in > conjunction with VFIO. The idea is that the userspace which is going to > run a guest may want to pre-register a user space memory region so > it all gets pinned once and never goes away. Having this done, > a hypervisor will not have to pin/unpin pages on every DMA map/unmap > request. This is going to help with multiple pinning of the same memory. > > Another use of it is in-kernel real mode (mmu off) acceleration of > DMA requests where real time translation of guest physical to host > physical addresses is non-trivial and may fail as linux ptes may be > temporarily invalid. Also, having cached host physical addresses > (compared to just pinning at the start and then walking the page table > again on every H_PUT_TCE), we can be sure that the addresses which we put > into TCE table are the ones we already pinned. > > This adds a list of memory regions to mm_context_t. Each region consists > of a header and a list of physical addresses. This adds API to: > 1. register/unregister memory regions; > 2. do final cleanup (which puts all pre-registered pages); > 3. do userspace to physical address translation; > 4. manage usage counters; multiple registration of the same memory > is allowed (once per container). > > This implements 2 counters per registered memory region: > - @mapped: incremented on every DMA mapping; decremented on unmapping; > initialized to 1 when a region is just registered; once it becomes zero, > no more mappings allowe; > - @used: incremented on every "register" ioctl; decremented on > "unregister"; unregistration is allowed for DMA mapped regions unless > it is the very last reference. For the very last reference this checks > that the region is still mapped and returns -EBUSY so the userspace > gets to know that memory is still pinned and unregistration needs to > be retried; @used remains 1. > > Host physical addresses are stored in vmalloc'ed array. In order to > access these in the real mode (mmu off), there is a real_vmalloc_addr() > helper. In-kernel acceleration patchset will move it from KVM to MMU code. > > Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx> There's a bunch of ways this could be cleaned up, but those can be done later. So, Reviewed-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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