Il 09/05/2013 02:53, liu ping fan ha scritto: > On Wed, May 8, 2013 at 11:44 PM, Paolo Bonzini <pbonz...@redhat.com> wrote: >> Il 08/05/2013 08:20, liu ping fan ha scritto: >>> On Mon, May 6, 2013 at 10:25 PM, Paolo Bonzini <pbonz...@redhat.com> wrote: >>>> Hi, >>>> >>>> this is an alternative approach to refactoring of dataplane's HostMem >>>> code. Here, I take Ping Fan's idea of RCU-style updating of the >>>> region list and apply it to the AddressSpace's FlatView. With this >>> >>> In fact, I am worrying about the priority of MemoryListener, if it is >>> true, then we should drop RCU-style idea. >> >> You mean in hostmem, or in general as in this patch? Note that this >> patch releases the old FlatView at the end of all MemoryListener operations. >> > Both in hostmem and this patch, they all broke the original design of > the MemoryListener, see notes for priority in code.
I think both hostmem and this patch are fine. The hypervisor is never involved, all accesses go through the "old" FlatView and regions cannot disappear thanks to ref/unref. In fact, we need _more_ RCU-style updates, not less. For BQL-less dispatch, address space mapping/translation can race against the MemoryListeners in exec.c. To fix this, phys_sections and AddressSpaceDispatch need to be reference counted and RCU-ified as well. Paolo > I have set out 2 patches to highlight this issue, and have CC you and > Stefanha. > > Regards, > Pingfan > >> Paolo >> >>> Also if it is true, there is >>> already a bug with hostmem listener. It should use region_del, not >>> region_nop to reconstruct the local view. But just let me have a deep >>> thinking. >>> >>> Regards, >>> Pingfan >>>> change, dataplane can simply use memory_region_find instead of >>>> hostmem. >>>> >>>> This is a somewhat larger change, but I prefer it for two reasons. >>>> >>>> 1) it splits the task of adding BQL-less memory dispatch in two parts, >>>> tacking memory_region_find first (which is simpler because locking >>>> is left to the caller). >>>> >>>> 2) HostMem duplicates a lot of the FlatView logic, and adding the >>>> RCU-style update in FlatView benefits everyone. >>>> >>>> The missing ingredients here are: >>>> >>>> 1) remember and unreference the MemoryRegions that are used in >>>> a vring entry. In order to implement this, it is probably simpler >>>> to change vring.c to use virtio.c's VirtQueueElement data structure. >>>> We want something like that anyway in order to support migration. >>>> >>>> 2) add an owner field to MemoryRegion, and set it for all MemoryRegions >>>> for hot-unpluggable devices. In this series, ref/unref are stubs. >>>> >>>> For simplicity I based the patches on my IOMMU rebase. I placed the >>>> tree at git://github.com/bonzini/qemu.git, branch iommu. >>>> >>>> Paolo >>>> >>>> Paolo Bonzini (8): >>>> memory: add ref/unref calls >>>> exec: check MRU in qemu_ram_addr_from_host >>>> memory: return MemoryRegion from qemu_ram_addr_from_host >>>> memory: ref/unref memory across address_space_map/unmap >>>> memory: access FlatView from a local variable >>>> memory: use a new FlatView pointer on every topology update >>>> memory: add reference counting to FlatView >>>> dataplane: replace hostmem with memory_region_find >>>> >>>> exec.c | 63 +++++++++--- >>>> hw/core/loader.c | 1 + >>>> hw/display/exynos4210_fimd.c | 6 + >>>> hw/display/framebuffer.c | 10 +- >>>> hw/i386/kvm/ioapic.c | 2 + >>>> hw/i386/kvmvapic.c | 1 + >>>> hw/misc/vfio.c | 2 + >>>> hw/virtio/dataplane/Makefile.objs | 2 +- >>>> hw/virtio/dataplane/hostmem.c | 176 >>>> --------------------------------- >>>> hw/virtio/dataplane/vring.c | 56 +++++++++-- >>>> hw/virtio/vhost.c | 2 + >>>> hw/virtio/virtio-balloon.c | 1 + >>>> hw/xen/xen_pt.c | 4 + >>>> include/exec/cpu-common.h | 2 +- >>>> include/exec/memory.h | 9 ++ >>>> include/hw/virtio/dataplane/hostmem.h | 57 ----------- >>>> include/hw/virtio/dataplane/vring.h | 3 +- >>>> kvm-all.c | 2 + >>>> memory.c | 142 +++++++++++++++++++++----- >>>> target-arm/kvm.c | 2 + >>>> target-i386/kvm.c | 4 +- >>>> target-sparc/mmu_helper.c | 1 + >>>> xen-all.c | 2 + >>>> 23 files changed, 253 insertions(+), 297 deletions(-) >>>> delete mode 100644 hw/virtio/dataplane/hostmem.c >>>> delete mode 100644 include/hw/virtio/dataplane/hostmem.h >>>> >>
