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

[Bathija, Pravin]

Dear Stephen,

I wanted to check-in about the v10 patch-set if there are items that need attention.  Also since there are SPDK and other open-source storage patches that are dependent on this feature, it would be great to have this merged soon, if everything looks good.

Regards,
Pravin


Internal Use - Confidential
> -----Original Message-----
> From: Bathija, Pravin
> Sent: Tuesday, April 7, 2026 3:44 PM
> To: 'Stephen Hemminger' <stephen at networkplumber.org>
> Cc: dev at dpdk.org; thomas at monjalon.net; maxime.coquelin at redhat.com;
> fengchengwen at huawei.com
> Subject: RE: [PATCH v9 0/5] Support add/remove memory region and get-max-
> slots
>
> Dear Stephen,
>
> The changes you suggested have been incorporated in the latest patch-set v10.
> Responses to comments inline.
>
> > -----Original Message-----
> > From: Stephen Hemminger <stephen at networkplumber.org>
> > Sent: Tuesday, April 7, 2026 7:21 AM
> > To: Bathija, Pravin <Pravin.Bathija at dell.com>
> > Cc: dev at dpdk.org; thomas at monjalon.net; maxime.coquelin at redhat.com;
> > fengchengwen at huawei.com
> > Subject: Re: [PATCH v9 0/5] Support add/remove memory region and
> > get-max- slots
> >
> >
> > [EXTERNAL EMAIL]
> >
> > On Tue, 7 Apr 2026 08:06:31 +0000
> > <pravin.bathija at dell.com> wrote:
> >
> > > From: Pravin M Bathija <pravin.bathija at 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.
> >
> Thanks for catching that — moved dev_invalidate_vrings after
> free_mem_region and the array compaction so that translate_ring_addresses
> 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.
>
> Again good catch, made the edit to the cover letter.