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). Thanks! > Thanks > > > > > > Thanks > > > > > > > > > > > To solve this, track GPA in the DMA entry that acs as unique identifiers > > > > to the maps. When the map needs to be removed, iova tree is able to > > > > find the right one. > > > > > > > > Users that does not go to this extra layer of indirection can use the > > > > iova tree as usual, with id = 0. > > > > > > > > This was found by Si-Wei Liu <si-wei....@oracle.com>, but I'm having a > > > > hard > > > > time to reproduce the issue. This has been tested only without > > > > overlapping > > > > maps. If it works with overlapping maps, it will be intergrated in the > > > > main > > > > series. > > > > > > > > Comments are welcome. Thanks! > > > > > > > > Eugenio Pérez (2): > > > > iova_tree: add an id member to DMAMap > > > > vdpa: identify aliased maps in iova_tree > > > > > > > > hw/virtio/vhost-vdpa.c | 2 ++ > > > > include/qemu/iova-tree.h | 5 +++-- > > > > util/iova-tree.c | 3 ++- > > > > 3 files changed, 7 insertions(+), 3 deletions(-) > > > > > > > > -- > > > > 2.44.0 > > > > > > > > > >
