Re: [PATCH v9 0/5] Support add/remove memory region and get-max-slots

[Stephen Hemminger <stephen@networkplumber.org>]

On Tue, 7 Apr 2026 08:06:31 +0000
<pravin.bathija@dell.com> wrote:

> From: Pravin M Bathija <pravin.bathija@dell.com>
> 
> This is version v9 of the patchset and it incorporates the
> recommendations made by Stephen Hemminger.
> 
> Changes made to patch 3/5
> - Restored max_guest_pages initial value to hardcoded 8 instead of
>   VHOST_MEMORY_MAX_NREGIONS, matching upstream semantics.
> 
> Changes made to patch 4/5
> - Added close(reg->fd) and reg->fd = -1 before goto close_msg_fds in the
>   mmap failure path to fix fd leak after fd was moved from ctx->fds[0].
> - Converted dev_invalidate_vrings from a plain function to a macro +
>   implementation function pair, accepting message ID as a parameter so
>   the static_assert reports the correct handler at each call site.
> - Updated dev_invalidate_vrings call in add_mem_reg to pass
>   VHOST_USER_ADD_MEM_REG as message ID.
> - Updated dev_invalidate_vrings call in rem_mem_reg to pass
>   VHOST_USER_ADD_MEM_REG as message ID.
> 
> This implementation has been extensively tested by doing Read/Write I/O
> from multiple instances of fio + libblkio (front-end) talking to
> spdk/dpdk (back-end) based drives. Tested with qemu front-end talking to
> dpdk testpmd (back-end) performing add/removal of memory regions. Also
> tested post-copy live migration after doing add_memory_region.
> 
> Version Log:
> Version v9 (Current version): Incorporate code review suggestions from
> Stephen Hemminger as described above.
> Version v8:  Incorporate code review suggestions from Stephen Hemminger.
> rewrite async_dma_map_region function to iterate guest pages by host
> address range matching
> change function dev_invalidate_vrings to accept a double pointer to
> propagate pointer updates
> new function remove_guest_pages was added
> add_mem_reg error path was narrowed to only clean up the single failed
> region instead of destroting all existing regions
> Version v7: Incorporate code review suggestions from Maxime Coquelin.
> Add debug messages to vhost_postcopy_register function.
> Version v6: Added the enablement of this feature as a final patch in
> this patch-set and other code optimizations as suggested by Maxime
> Coquelin.
> Version v5: removed the patch that increased the number of memory regions
> from 8 to 128. This will be submitted as a separate feature at a later
> point after incorporating additional optimizations. Also includes code
> optimizations as suggested by Feng Cheng Wen.
> Version v4: code optimizations as suggested by Feng Cheng Wen.
> Version v3: code optimizations as suggested by Maxime Coquelin
> and Thomas Monjalon.
> Version v2: code optimizations as suggested by Maxime Coquelin.
> Version v1: Initial patch set.
> 
> Pravin M Bathija (5):
>   vhost: add user to mailmap and define to vhost hdr
>   vhost_user: header defines for add/rem mem region
>   vhost_user: support function defines for back-end
>   vhost_user: Function defs for add/rem mem regions
>   vhost_user: enable configure memory slots
> 
>  .mailmap               |   1 +
>  lib/vhost/rte_vhost.h  |   4 +
>  lib/vhost/vhost_user.c | 403 ++++++++++++++++++++++++++++++++++++-----
>  lib/vhost/vhost_user.h |  10 +
>  4 files changed, 375 insertions(+), 43 deletions(-)
> 

AI review is mostly clean now.

Patch series looks good overall. One issue in 4/5:
In rem_mem_reg, dev_invalidate_vrings (which calls
translate_ring_addresses) runs while the region being removed is still
mapped. Any vring address that resolves into that region will get a
pointer that becomes invalid after the subsequent
free_mem_region/munmap. Consider freeing the region first so translate
only sees surviving regions.

Also minor: the v9 cover letter changelog says rem_mem_reg passes
VHOST_USER_ADD_MEM_REG but the code correctly uses
VHOST_USER_REM_MEM_REG — just a typo in the changelog.