Dear Stephen, Thank you for the quick review. I have just submitted an updated patch set v9 with the changes that were suggested. The responses to your comments are inline.
Internal Use - Confidential > -----Original Message----- > From: Stephen Hemminger <[email protected]> > Sent: Sunday, April 5, 2026 4:30 PM > To: Bathija, Pravin <[email protected]> > Cc: [email protected]; [email protected]; [email protected]; > [email protected] > Subject: Re: [PATCH v8 0/5] Support add/remove memory region and get-max- > slots > > > [EXTERNAL EMAIL] > > On Fri, 3 Apr 2026 01:54:29 +0000 > <[email protected]> wrote: > > > From: Pravin M Bathija <[email protected]> > > > > This is version v8 of the patchset and it incorporates the > > recommendations made by Stephen Hemminger. > > The async_dma_map_region function was rewritten to iterate guest pages > > by host address range matching rather than assuming contiguous array > > indices after sorting, and now returns an error code so that DMA > > mapping failures are treated as fatal during add_mem_reg. The > > dev_invalidate_vrings function was changed to accept a double pointer > > to propagate pointer updates from numa_realloc through > > translate_ring_addresses, preventing a user-after-free in both > > add_mem_reg and rem_mem_reg callers. > > > > A new remove_guest_pages function was added to clean up stale guest > > page entries when removing a region. The rem_mem_reg handler now > > compacts the regions array using memmove after removal, keeping it > > contiguous so that all existing nregions-based iteration in address > > translation functions like qva_to_vva and hva_togpa continues to work > > correctly. This compaction also eliminates the need for the > > guest_user_addr == 0 free-slot sentinel in add_mem_reg, which was > > problematic since guest virtual address zero is valid. > > > > The add_mem_reg error path was narrowed to only clean up the single > > failed region instead of destroying all existing regions. A missing > > ctx->fds[0] = -1 assignment was added after the fd handoff to prevent > > double-close on error paths. The overlap check was corrected to use > > region size instead of mmap_size, which included alignment padding and > > caused false positives. The rem_mem_reg handler registration was fixed > > to accept file descriptors as required by the vhost-user protocol, > > with proper fd cleanup added in all exit paths. Finally, the postcopy > > registration in add_mem_reg was changed to call > > vhost_user_postcopy_region_register directly for the single new > > region, avoiding the use of vhost_user_postcopy_register which reads > > the wrong payload union member, and a defensive guard was added to > > vhost_user_initialize_memory against double initialization. > > > > 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 v8 (Current version): Incorporate code review suggestions from > > Stephen Hemminger as described above. > > 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 | 392 > > ++++++++++++++++++++++++++++++++++++----- > > lib/vhost/vhost_user.h | 10 ++ > > 4 files changed, 364 insertions(+), 43 deletions(-) > > > > AI still finds a number of issues. > > Patches 1/5, 2/5, and 5/5 look fine. > > In patch 4/5, there is an fd leak in vhost_user_add_mem_reg() when > vhost_user_mmap_region() fails. The fd has already been moved from > ctx->fds[0] into reg->fd (and ctx->fds[0] set to -1) before the > mmap call. On failure the goto lands at close_msg_fds which only closes ctx- > >fds[] (all -1 at that point). The fd in reg->fd is never closed because > free_mem_region() is not reached (it guards on reg->mmap_addr which mmap > never set). Suggest adding > close(reg->fd) before the goto, or introducing a cleanup label. Fixed by adding close(reg->fd) and reg->fd = -1 before the goto close_msg_fds in the mmap failure path. This closes the fd that was already moved out of ctx->fds[0] and ensures it is not leaked. > > Also in patch 4/5, dev_invalidate_vrings() hardcodes > VHOST_USER_ASSERT_LOCK(dev, vq, VHOST_USER_ADD_MEM_REG) but is > called from both add_mem_reg and rem_mem_reg. The static_assert passes > because both handlers set lock_all_qps = true, but the debug assertion message > will report the wrong message ID on the remove path. Consider passing the > message ID as a parameter. Fixed. Converted dev_invalidate_vrings into a macro plus implementation function pair. The macro accepts the message ID as a parameter and performs the static_assert with the correct token at the call site, then calls _dev_invalidate_vrings() for the actual work. The add_mem_reg caller passes VHOST_USER_ADD_MEM_REG and the rem_mem_reg caller passes VHOST_USER_REM_MEM_REG, so the debug assertion message always reports the correct handler. > > Minor: in patch 3/5, vhost_user_initialize_memory() uses > VHOST_MEMORY_MAX_NREGIONS as max_guest_pages. Upstream uses a > hardcoded 8 for this. The two values happen to be equal today but have > different semantics — max_guest_pages is about hugepage tracking > granularity, not region count. Agreed. Restored to the upstream hardcoded value of 8. The guest_pages array grows dynamically via add_one_guest_page when it fills up, so this is just the initial allocation size and should not be coupled to the region count constant.
