[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 3/5] tools/libxendevicemodel: extract functions and add a compat layer
On 22/02/17 14:37, Ian Jackson wrote: > Andrew Cooper writes ("Re: [Xen-devel] [PATCH v2 3/5] > tools/libxendevicemodel: extract functions and add a compat layer"): >> On 22/02/17 14:20, Ian Jackson wrote: >>> As I think we discussed some time last week (?), this function cannot >>> be a DMOP. This is because enabling track_dirty_vram causes the >>> hypervisor to remember the memory referred to by dirty_bitmap, but the >>> dmop privcmd restriction mechanism only guarantees that the memory is >>> valid and belonging to this guest _during the hypercall_. >> Sorry to jump in here, but what? Since when? > Maybe I have misunderstood. > >> track-dirty-vram stashes where the DM thinks the vram is in guest >> physical address space, so if a new range is requested, we can set >> appropriate bits in the dirty map. > Does this ... > >>>> + return xendevicemodel_op(dmod, domid, 2, &op, sizeof(op), >>>> + dirty_bitmap, (size_t)(nr + 7) / 8); >>>> +} > ... not result in the hypervisor asynchronously updating the contents > of dirty_bitmap[whatever], later ? No. > >> However, the interesting pointer for the DMOP (i.e. where the DM would >> like Xen to write the bitmap to) is not stored across distinct calls at >> all. It is stored as part of a continuation, but that is still >> logically part of a single invocation. > Is the bitmap copied in each dmop call ? Yes, and hence... ... one optimisation I want to do in the future is for the DM to be able to make a Read-only mapping of Xens logdirty bitmap, so the bitmap can be passed by shared memory rather than memcpy(), because I expect it would be rather more efficient during some of the time-sensitive bits of live migrate. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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