On Mon, May 13, 2024 at 10:28 AM Jason Wang <jasow...@redhat.com> wrote: > > On Mon, May 13, 2024 at 2:28 PM Eugenio Perez Martin > <epere...@redhat.com> wrote: > > > > On Sat, May 11, 2024 at 6:07 AM Jason Wang <jasow...@redhat.com> wrote: > > > > > > On Fri, May 10, 2024 at 3:16 PM Eugenio Perez Martin > > > <epere...@redhat.com> wrote: > > > > > > > > On Fri, May 10, 2024 at 6:29 AM Jason Wang <jasow...@redhat.com> wrote: > > > > > > > > > > On Thu, May 9, 2024 at 3:10 PM Eugenio Perez Martin > > > > > <epere...@redhat.com> wrote: > > > > > > > > > > > > On Thu, May 9, 2024 at 8:27 AM Jason Wang <jasow...@redhat.com> > > > > > > wrote: > > > > > > > > > > > > > > On Thu, May 9, 2024 at 1:16 AM Eugenio Perez Martin > > > > > > > <epere...@redhat.com> wrote: > > > > > > > > > > > > > > > > On Wed, May 8, 2024 at 4:29 AM Jason Wang <jasow...@redhat.com> > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > On Tue, May 7, 2024 at 6:57 PM Eugenio Perez Martin > > > > > > > > > <epere...@redhat.com> wrote: > > > > > > > > > > > > > > > > > > > > On Tue, May 7, 2024 at 9:29 AM Jason Wang > > > > > > > > > > <jasow...@redhat.com> wrote: > > > > > > > > > > > > > > > > > > > > > > On Fri, Apr 12, 2024 at 3:56 PM Eugenio Perez Martin > > > > > > > > > > > <epere...@redhat.com> wrote: > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Apr 12, 2024 at 8:47 AM Jason Wang > > > > > > > > > > > > <jasow...@redhat.com> wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > On Wed, Apr 10, 2024 at 6:03 PM Eugenio Pérez > > > > > > > > > > > > > <epere...@redhat.com> wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > The guest may have overlapped memory regions, where > > > > > > > > > > > > > > different GPA leads > > > > > > > > > > > > > > to the same HVA. This causes a problem when > > > > > > > > > > > > > > overlapped regions > > > > > > > > > > > > > > (different GPA but same translated HVA) exists in > > > > > > > > > > > > > > the tree, as looking > > > > > > > > > > > > > > them by HVA will return them twice. > > > > > > > > > > > > > > > > > > > > > > > > > > I think I don't understand if there's any side effect > > > > > > > > > > > > > for shadow virtqueue? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > My bad, I totally forgot to put a reference to where > > > > > > > > > > > > this comes from. > > > > > > > > > > > > > > > > > > > > > > > > Si-Wei found that during initialization this sequences > > > > > > > > > > > > of maps / > > > > > > > > > > > > unmaps happens [1]: > > > > > > > > > > > > > > > > > > > > > > > > HVA GPA IOVA > > > > > > > > > > > > ------------------------------------------------------------------------------------------------------------------------- > > > > > > > > > > > > Map > > > > > > > > > > > > [0x7f7903e00000, 0x7f7983e00000) [0x0, 0x80000000) > > > > > > > > > > > > [0x1000, 0x80000000) > > > > > > > > > > > > [0x7f7983e00000, 0x7f9903e00000) [0x100000000, > > > > > > > > > > > > 0x2080000000) > > > > > > > > > > > > [0x80001000, 0x2000001000) > > > > > > > > > > > > [0x7f7903ea0000, 0x7f7903ec0000) [0xfeda0000, > > > > > > > > > > > > 0xfedc0000) > > > > > > > > > > > > [0x2000001000, 0x2000021000) > > > > > > > > > > > > > > > > > > > > > > > > Unmap > > > > > > > > > > > > [0x7f7903ea0000, 0x7f7903ec0000) [0xfeda0000, > > > > > > > > > > > > 0xfedc0000) [0x1000, > > > > > > > > > > > > 0x20000) ??? > > > > > > > > > > > > > > > > > > > > > > > > The third HVA range is contained in the first one, but > > > > > > > > > > > > exposed under a > > > > > > > > > > > > different GVA (aliased). This is not "flattened" by > > > > > > > > > > > > QEMU, as GPA does > > > > > > > > > > > > not overlap, only HVA. > > > > > > > > > > > > > > > > > > > > > > > > At the third chunk unmap, the current algorithm finds > > > > > > > > > > > > the first chunk, > > > > > > > > > > > > not the second one. This series is the way to tell the > > > > > > > > > > > > difference at > > > > > > > > > > > > unmap time. > > > > > > > > > > > > > > > > > > > > > > > > [1] > > > > > > > > > > > > https://lists.nongnu.org/archive/html/qemu-devel/2024-04/msg00079.html > > > > > > > > > > > > > > > > > > > > > > > > Thanks! > > > > > > > > > > > > > > > > > > > > > > Ok, I was wondering if we need to store GPA(GIOVA) to HVA > > > > > > > > > > > mappings in > > > > > > > > > > > the iova tree to solve this issue completely. Then there > > > > > > > > > > > won't be > > > > > > > > > > > aliasing issues. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I'm ok to explore that route but this has another problem. > > > > > > > > > > Both SVQ > > > > > > > > > > vrings and CVQ buffers also need to be addressable by > > > > > > > > > > VhostIOVATree, > > > > > > > > > > and they do not have GPA. > > > > > > > > > > > > > > > > > > > > At this moment vhost_svq_translate_addr is able to handle > > > > > > > > > > this > > > > > > > > > > transparently as we translate vaddr to SVQ IOVA. How can we > > > > > > > > > > store > > > > > > > > > > these new entries? Maybe a (hwaddr)-1 GPA to signal it has > > > > > > > > > > no GPA and > > > > > > > > > > then a list to go through other entries (SVQ vaddr and CVQ > > > > > > > > > > buffers). > > > > > > > > > > > > > > > > > > This seems to be tricky. > > > > > > > > > > > > > > > > > > As discussed, it could be another iova tree. > > > > > > > > > > > > > > > > > > > > > > > > > Yes but there are many ways to add another IOVATree. Let me > > > > > > > > expand & recap. > > > > > > > > > > > > > > > > Option 1 is to simply add another iova tree to > > > > > > > > VhostShadowVirtqueue. > > > > > > > > Let's call it gpa_iova_tree, as opposed to the current > > > > > > > > iova_tree that > > > > > > > > translates from vaddr to SVQ IOVA. To know which one to use is > > > > > > > > easy at > > > > > > > > adding or removing, like in the memory listener, but how to > > > > > > > > know at > > > > > > > > vhost_svq_translate_addr? > > > > > > > > > > > > > > Then we won't use virtqueue_pop() at all, we need a SVQ version of > > > > > > > virtqueue_pop() to translate GPA to SVQ IOVA directly? > > > > > > > > > > > > > > > > > > > The problem is not virtqueue_pop, that's out of the > > > > > > vhost_svq_translate_addr. The problem is the need of adding > > > > > > conditionals / complexity in all the callers of > > > > > > > > > > > > > > > > > > > > > > The easiest way for me is to rely on memory_region_from_host(). > > > > > > > > When > > > > > > > > vaddr is from the guest, it returns a valid MemoryRegion. When > > > > > > > > it is > > > > > > > > not, it returns NULL. I'm not sure if this is a valid use case, > > > > > > > > it > > > > > > > > just worked in my tests so far. > > > > > > > > > > > > > > > > Now we have the second problem: The GPA values of the regions > > > > > > > > of the > > > > > > > > two IOVA tree must be unique. We need to be able to find > > > > > > > > unallocated > > > > > > > > regions in SVQ IOVA. At this moment there is only one IOVATree, > > > > > > > > so > > > > > > > > this is done easily by vhost_iova_tree_map_alloc. But it is very > > > > > > > > complicated with two trees. > > > > > > > > > > > > > > Would it be simpler if we decouple the IOVA allocator? For > > > > > > > example, we > > > > > > > can have a dedicated gtree to track the allocated IOVA ranges. It > > > > > > > is > > > > > > > shared by both > > > > > > > > > > > > > > 1) Guest memory (GPA) > > > > > > > 2) SVQ virtqueue and buffers > > > > > > > > > > > > > > And another gtree to track the GPA to IOVA. > > > > > > > > > > > > > > The SVQ code could use either > > > > > > > > > > > > > > 1) one linear mappings that contains both SVQ virtqueue and > > > > > > > buffers > > > > > > > > > > > > > > or > > > > > > > > > > > > > > 2) dynamic IOVA allocation/deallocation helpers > > > > > > > > > > > > > > So we don't actually need the third gtree for SVQ HVA -> SVQ IOVA? > > > > > > > > > > > > > > > > > > > That's possible, but that scatters the IOVA handling code instead of > > > > > > keeping it self-contained in VhostIOVATree. > > > > > > > > > > To me, the IOVA range/allocation is orthogonal to how IOVA is used. > > > > > > > > > > An example is the iova allocator in the kernel. > > > > > > > > > > Note that there's an even simpler IOVA "allocator" in NVME passthrough > > > > > code, not sure it is useful here though (haven't had a deep look at > > > > > that). > > > > > > > > > > > > > I don't know enough about them to have an opinion. I keep seeing the > > > > drawback of needing to synchronize both allocation & adding in all the > > > > places we want to modify the IOVATree. At this moment, these are the > > > > vhost-vdpa memory listener, the SVQ vring creation and removal, and > > > > net CVQ buffers. But it may be more in the future. > > > > > > > > What are the advantages of keeping these separated that justifies > > > > needing to synchronize in all these places, compared with keeping them > > > > synchronized in VhostIOVATree? > > > > > > It doesn't need to be synchronized. > > > > > > Assuming guest and SVQ shares IOVA range. IOVA only needs to track > > > which part of the range has been used. > > > > > > > Not sure if I follow, that is what I mean with "synchronized". > > Oh right. > > > > > > This simplifies things, we can store GPA->IOVA mappings and SVQ -> > > > IOVA mappings separately. > > > > > > > Sorry, I still cannot see the whole picture :). > > > > Let's assume we have all the GPA mapped to specific IOVA regions, so > > we have the first IOVA tree (GPA -> IOVA) filled. Now we enable SVQ > > because of the migration. How can we know where we can place SVQ > > vrings without having them synchronized? > > Just allocating a new IOVA range for SVQ? > > > > > At this moment we're using a tree. The tree nature of the current SVQ > > IOVA -> VA makes all nodes ordered so it is more or less easy to look > > for holes. > > Yes, iova allocate could still be implemented via a tree. > > > > > Now your proposal uses the SVQ IOVA as tree values. Should we iterate > > over all of them, order them, of the two trees, and then look for > > holes there? > > Let me clarify, correct me if I was wrong: > > 1) IOVA allocator is still implemented via a tree, we just don't need > to store how the IOVA is used > 2) A dedicated GPA -> IOVA tree, updated via listeners and is used in > the datapath SVQ translation > 3) A linear mapping or another SVQ -> IOVA tree used for SVQ >
Ok, so the part I was missing is that now we have 3 whole trees, with somehow redundant information :). In some sense this is simpler than trying to get all the information from only two trees. On the bad side, all SVQ calls that allocate some region need to remember to add to one of the two other threes. That is what I mean by synchronized. But sure, we can go that way. > Thanks > > > > > > Thanks > > > > > > > > > > > Thanks! > > > > > > > > > >
