[Qemu-devel] [PATCH v3 00/12] intel-iommu: nested vIOMMU, cleanups, bug fixes

[Peter Xu]

(Hello, Jintack, Feel free to test this branch again against your scp
 error case when you got free time)

I rewrote some of the patches in V3.  Major changes:

- Dropped mergable interval tree, instead introduced IOVA tree, which
  is even simpler.

- Fix the scp error issue that Jintack reported.  Please see patches
  for detailed information.  That's the major reason to rewrite a few
  of the patches.  We use replay for domain flushes are possibly
  incorrect in the past.  The thing is that IOMMU replay has an
  "definition" that "we should only send MAP when new page detected",
  while for shadow page syncing we actually need something else than
  that.  So in this version I started to use a new
  vtd_sync_shadow_page_table() helper to do the page sync.

- Some other refines after the refactoring.

I'll add unit test for the IOVA tree after this series merged to make
sure we won't switch to another new tree implementaion...

The element size in the new IOVA tree should be around
sizeof(GTreeNode + IOMMUTLBEntry) ~= (5*8+4*8) = 72 bytes.  So the
worst case usage ratio would be 72/4K=2%, which still seems acceptable
(it means 8G L2 guest will use 8G*2%=160MB as metadata to maintain the
mapping in QEMU).

I did explicit test with scp this time, copying 1G sized file for >10
times on each of the following case:

- L1 guest, with vIOMMU and with assigned device
- L2 guest, without vIOMMU and with assigned device
- L2 guest, with vIOMMU (so 3-layer nested IOMMU) and with assigned device

Please review.  Thanks,

(Below are old content from previous cover letter)

==========================

v2:
- fix patchew code style warnings
- interval tree: postpone malloc when inserting; simplify node remove
  a bit where proper [Jason]
- fix up comment and commit message for iommu lock patch [Kevin]
- protect context cache too using the iommu lock [Kevin, Jason]
- add vast comment in patch 8 to explain the modify-PTE problem
  [Jason, Kevin]

Online repo:

  https://github.com/xzpeter/qemu/tree/fix-vtd-dma

This series fixes several major problems that current code has:

- Issue 1: when getting very big PSI UNMAP invalidations, the current
  code is buggy in that we might skip the notification while actually
  we should always send that notification.

- Issue 2: IOTLB is not thread safe, while block dataplane can be
  accessing and updating it in parallel.

- Issue 3: For devices that only registered with UNMAP-only notifiers,
  we don't really need to do page walking for PSIs, we can directly
  deliver the notification down.  For example, vhost.

- Issue 4: unsafe window for MAP notified devices like vfio-pci (and
  in the future, vDPA as well).  The problem is that, now for domain
  invalidations we do this to make sure the shadow page tables are
  correctly synced:

  1. unmap the whole address space
  2. replay the whole address space, map existing pages

  However during step 1 and 2 there will be a very tiny window (it can
  be as big as 3ms) that the shadow page table is either invalid or
  incomplete (since we're rebuilding it up).  That's fatal error since
  devices never know that happending and it's still possible to DMA to
  memories.

Patch 1 fixes issue 1.  I put it at the first since it's picked from
an old post.

Patch 2 is a cleanup to remove useless IntelIOMMUNotifierNode struct.

Patch 3 fixes issue 2.

Patch 4 fixes issue 3.

Patch 5-9 fix issue 4.  Here a very simple interval tree is
implemented based on Gtree.  It's different with general interval tree
in that it does not allow user to pass in private data (e.g.,
translated addresses).  However that benefits us that then we can
merge adjacent interval leaves so that hopefully we won't consume much
memory even if the mappings are a lot (that happens for nested virt -
when mapping the whole L2 guest RAM range, it can be at least in GBs).

Patch 10 is another big cleanup only can work after patch 9.

Tests:

- device assignments to L1, even L2 guests.  With this series applied
  (and the kernel IOMMU patches: https://lkml.org/lkml/2018/4/18/5),
  we can even nest vIOMMU now, e.g., we can specify vIOMMU in L2 guest
  with assigned devices and things will work.  We can't before.

- vhost smoke test for regression.

Please review.  Thanks,

Peter Xu (12):
  intel-iommu: send PSI always even if across PDEs
  intel-iommu: remove IntelIOMMUNotifierNode
  intel-iommu: add iommu lock
  intel-iommu: only do page walk for MAP notifiers
  intel-iommu: introduce vtd_page_walk_info
  intel-iommu: pass in address space when page walk
  intel-iommu: trace domain id during page walk
  util: implement simple iova tree
  intel-iommu: maintain per-device iova ranges
  intel-iommu: simplify page walk logic
  intel-iommu: new vtd_sync_shadow_page_table_range
  intel-iommu: new sync_shadow_page_table

 include/hw/i386/intel_iommu.h |  19 +-
 include/qemu/iova-tree.h      | 134 ++++++++++++
 hw/i386/intel_iommu.c         | 381 +++++++++++++++++++++++++---------
 util/iova-tree.c              | 114 ++++++++++
 MAINTAINERS                   |   6 +
 hw/i386/trace-events          |   5 +-
 util/Makefile.objs            |   1 +
 7 files changed, 556 insertions(+), 104 deletions(-)
 create mode 100644 include/qemu/iova-tree.h
 create mode 100644 util/iova-tree.c

-- 
2.17.0