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

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

On 23/10/2026 17:14, Tu Dinh wrote:
> 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.
> 

There's a deadlock somewhere in this series, I'm looking for it. I'll 
send a v2.

> 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(-)
> 



--
Ngoc Tu Dinh | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

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