Hi Stephen, Thank you for your feedback on the patch-set. I have submitted v14 incorporating the changes you suggested. The responses to your comments are inline.
Internal Use - Confidential > -----Original Message----- > From: Stephen Hemminger <[email protected]> > Sent: Monday, May 18, 2026 10:14 AM > To: Bathija, Pravin <[email protected]> > Cc: [email protected]; [email protected]; > [email protected]; [email protected] > Subject: Re: [PATCH v13 0/5] Support add/remove memory region and get-max- > slots > > > [EXTERNAL EMAIL] > > On Thu, 14 May 2026 02:01:52 +0000 > <[email protected]> wrote: > > > From: Pravin M Bathija <[email protected]> > > > > This is version v13 of the patchset and it incorporates the > > recommendations made by Fengcheng Wen. > > > > Changes made to patch 3/5 and 4/5 > > * Relocated function remove_guest_pages from patch 3/5 to 4/5. > > * Renamed VhostUserSingleMemReg to VhostUserMemRegMsg and > memory_single > > to memreg. > > > > 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 v13 (Current version): Incorporate code review suggestions > > from Fengcheng Wen as described above. > > Version v12: Incorporate code review suggestions from Maxime Coquelin > > and ai-code-review. > > Changes made to patch 3/5 > > Refactored async_dma_map() to delegate to async_dma_map_region(), > > eliminating code duplication between the two functions. > > Restored original comments in async_dma_map_region() explaining why > > ENODEV and EINVAL errors are ignored (these were stripped in v10) > > Reverted unnecessary changes to vhost_user_postcopy_register() -- > > removed the host_user_addr == 0 checks and reg_msg_index indirection > > that were added in v10, since this function is only called from > > vhost_user_set_mem_table() where regions are always contiguous. > > > > Version v11: Incorporate code review suggestions from Stephen Hemminger. > > Change made to patch 4/5 > > Fix incomplete cleanup in vhost_user_add_mem_reg() when > > vhost_user_mmap_region() fails after the mmap succeeds (e.g. > > add_guest_pages() realloc failure) realloc failure). The error path > > now calls remove_guest_pages() and free_mem_region() to undo the > > mapping and stale guest-page entries, preventing a leaked mmap and > > slot reuse corruption. The plain close(fd) path is kept for pre-mmap > > failures. > > > > Version v10: Incorporate code review suggestions from Stephen Hemminger. > > Change made to patch 4/5 > > Moved dev_invalidate_vrings after free_mem_region, array compaction, > > and nregions decrement. This ensures translate_ring_addresses only > > sees surviving memory regions, preventing vring pointers from > > resolving into a region that is about to be unmapped. > > > > Version v9: Incorporate code review suggestions from 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_REM_MEM_REG as message ID. > > > > 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 | 418 > > +++++++++++++++++++++++++++++++++++------ > > lib/vhost/vhost_user.h | 10 + > > 4 files changed, 371 insertions(+), 62 deletions(-) > > > > Some useful AI feedback > > Review of [PATCH v13 0-5/5] vhost: configure memory slots support > Author: Pravin M Bathija <[email protected]> > > This revision addresses essentially every correctness issue raised in the > v7-v12 > reviews: > > - ctx->fds[0] = -1 ownership transfer is now done before mmap, and > the mmap-failure path closes reg->fd explicitly when mmap never > set reg->mmap_addr. > - _dev_invalidate_vrings now takes struct virtio_net **pdev and > writes back *pdev = dev at the end, so a numa_realloc inside > translate_ring_addresses propagates correctly. Both call sites > refresh "dev = *pdev;" afterwards. > - The dev_invalidate_vrings() macro now takes the message id and > uses static_assert(id ## _LOCK_ALL_QPS, ...), matching the > existing VHOST_USER_ASSERT_LOCK pattern. Works for both > VHOST_USER_ADD_MEM_REG and VHOST_USER_REM_MEM_REG call sites. > - Overlap check in vhost_user_add_mem_reg uses guest address > space (guest_user_addr, size / userspace_addr, memory_size), > no longer mmap_size. > - free_new_region undoes only the failed region: async DMA unmap, > remove_guest_pages, free_mem_region(reg), nregions--. > - async_dma_map_region iterates dev->nr_guest_pages and filters > by [reg_start, reg_end), eliminating the prior reg_size > underflow loop. > - The regions array is kept contiguous via memmove on REM_MEM_REG, > so existing iterators that walk mem->nregions remain correct. > - max_guest_pages is back to 8 in vhost_user_initialize_memory. > > One protocol-level issue remains worth raising. > > > Patch 4/5 -- vhost_user: Function defs for add/rem mem regions > -------------------------------------------------------------------- > > Warning: ADD_MEM_REG does not send the host_user_addr reply > > Per the vhost-user spec for VHOST_USER_ADD_MEM_REG, the back-end > is expected to reply with the same message format and the > userspace_addr field replaced by the host userspace address that > the region was mapped into. The handler returns > RTE_VHOST_MSG_RESULT_OK with no reply constructed, so the > dispatcher does not call send_vhost_reply(). > > For postcopy migration this matters in particular: the original > vhost_user_postcopy_register() does two things -- exchange the > host_user_addr with the front-end and wait for an ack, then > register the regions with userfaultfd. The patch only does the > userfaultfd registration via vhost_user_postcopy_region_register(). > The in-code comment notes the payload-layout mismatch with > vhost_user_postcopy_register() but stops there. > > Without the address reply, QEMU will not know the back-end's > mapping for regions added via ADD_MEM_REG, so the userfaultfd > handling on the QEMU side cannot resolve faults in those > regions. Postcopy migration combined with the > CONFIGURE_MEM_SLOTS feature will not work. > > Suggested fix: construct a memreg-payload reply with > region->userspace_addr replaced by reg->host_user_addr and > return RTE_VHOST_MSG_RESULT_REPLY. At minimum, refuse > ADD_MEM_REG when dev->postcopy_listening is set, so that the > combination fails cleanly rather than silently mis-mapping. Fixed, now constructs a memreg reply with host_user_addr and returns RTE_VHOST_MSG_RESULT_REPLY. > > > Info: vhost_user_rem_mem_reg does not validate ctx->fd_num > > The handler is registered with accepts_fd = true and does not > call validate_msg_fds(). The trailing close_msg_fds(ctx) cleans > up whatever fds were passed, so this is not a leak, but a > malformed message with an unexpected fd count is silently > accepted. The other accepts_fd handlers in this file validate > fd_num explicitly. Fixed, added validate_msg_fds(dev, ctx, 0). > > > Info: vhost_user_get_max_mem_slots cast is unnecessary > > ctx->msg.payload.u64 = (uint64_t)max_mem_slots; > > max_mem_slots is uint32_t and the assignment widens > automatically; the cast can be dropped. Minor. Dropped the cast. > > > Reviewed-by would be appropriate once the postcopy reply is addressed (or the > combination is rejected). The rest of the series looks correct. Added the Reviewed-by line in v14
