[RFC PATCH 0/9] Defer completion and ring destruction until backend grant release

[Tu Dinh <ngoc-tu.dinh@xxxxxxxxxx>]

Hello,

When a backend is accessing a grant entry, it'll set the GTF_reading|
GTF_writing bits on that entry. RevokeForeignAccess will fail as long as
these bits are still set.

WinPV drivers assume that you can ignore RevokeForeignAccess failures
after a certain number of retries. This is unfortunately not the case,
as backends can still access the grants and corrupt things. We've
observed data corruption that we suspect as being caused by this issue.

This series attempts to clarify the fallible nature of
RevokeForeignAccess, and fixes the problem by deferring request
completion and ring destruction until after the corresponding grants
have been released by the backend.

It's freshly written and will undergo testing on our side, but I'd
appreciate if you could test this series on your testing infrastructure
as well to reveal any early errors.

This is the first series of fix for a class of similar issues. Further
fixes will be needed in other drivers using the grant interface (esp.
XenVif, XenIface); there are also other issues that have not been
discussed in this series.

Tu Dinh (9):
  granter: Correct the accounting of Current
  Use GNTTAB_INTERFACE_V5
  frontend: Initialize the granter before the ring
  granter: Split GranterTryPut to its own function
  granter: Decouple cache lifetime from Connected
  granter: Introduce GranterD0ToD3/D3ToD0
  ring: Introduce RingD3ToD0/RingD0ToD3
  ring: Defer destruction until backend grant release
  ring: Defer request completion until backend grant release

 include/gnttab_interface.h |  90 +++--
 src/xenvbd.inf             |   6 +-
 src/xenvbd/frontend.c      |  63 ++--
 src/xenvbd/frontend.h      |   4 +-
 src/xenvbd/granter.c       | 173 +++++++---
 src/xenvbd/granter.h       |  17 +-
 src/xenvbd/ring.c          | 662 +++++++++++++++++++++++++++++--------
 src/xenvbd/ring.h          |  13 +
 8 files changed, 807 insertions(+), 221 deletions(-)

-- 
2.56.0.windows.3



--
Ngoc Tu Dinh | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech