Reduce number of allocations sending memory state.

Implement and use new Xen and Linux kernel ABI to copy foreign memory.
This new ABI allows to replace the expensive  map/copy/unmap sequence
with a single call.

Changes since v1:
- add commit to cache up to 4 pages in hypercall;
- add other 2 commits reducing chunks passed to write/writev.

Changes since v2:
- update patches commit prefixes;
- add other 2 optisations.

Changes since v3:
- address some comments;
- add patches for foreign copy optimisation.

Changes since v4:
- added Reviewed-by;
- improved commit messages;
- other minor fixes, see individual commits.

Changes since v5:
- avoids potential buffer underflow if nr_pages is 0 calling cache_alloc;
- do not overwrite errno if xenforeignmemory_map fails;
- lot of changes to "implement new foreign copy hypercall", see specific
  commit.

Changes since v6:
- removed merged patch;
- keep only optimization commits for now;
- improve comments;
- merged "fill directly iov structure collapsing them" and moved it;
- split "allocate various migration arrays just once";
- add a commit for memory checks using Valgrind.

Changes since v7:
- removed merged commits;
- minor style fixes.

Changes since v8:
- added Reviewed-by;
- remove useless check;
- remove useless memset;
- initialize variables while declaring them.

Changes since v9:
- add back commits for foreign copy;
- rework page permissions check;
- do not limit domain for new hypercall;
- add back some memory check using Valgrind and sanitizers;
- fixed compatibility for ARM;
- minor fixes.

Edwin Török (3):
  libs/call: cache up to 4 pages in hypercall bounce buffers
  libs/guest: allocate various migration arrays just once
  libs/guest: use foreign copy API during migration

Frediano Ziglio (6):
  libs/guest: move batch_pfns into a separate structure
  libs/guest: use Valgrind or sanitizers to detect various buffer
    overflows
  libs/guest: add xg_foreignmemory_copy_{from,to}
  xen: implement new foreign copy hypercall
  privcmd: Add definition for new Linux privcmd to access new Xen
    hypercall
  libs/guest: use new hypercall if available

 tools/config.h.in                     |   6 ++
 tools/configure                       |  12 +++
 tools/configure.ac                    |   3 +-
 tools/include/xen-sys/Linux/privcmd.h |  10 ++
 tools/libs/call/buffer.c              |  34 ++++--
 tools/libs/call/core.c                |   3 +-
 tools/libs/call/private.h             |   8 +-
 tools/libs/ctrl/xc_private.h          |  61 ++++++++++-
 tools/libs/guest/xg_sr_common.c       |  86 +++++++++++++++
 tools/libs/guest/xg_sr_common.h       |  25 ++++-
 tools/libs/guest/xg_sr_restore.c      |  78 +++++++-------
 tools/libs/guest/xg_sr_save.c         | 134 +++++++++++------------
 xen/common/memory.c                   | 149 ++++++++++++++++++++++++++
 xen/include/public/memory.h           |  45 +++++++-
 xen/include/xsm/dummy.h               |  14 +++
 xen/include/xsm/hooks.h               |   2 +
 xen/xsm/flask/hooks.c                 |  10 ++
 17 files changed, 552 insertions(+), 128 deletions(-)

-- 
2.43.0

On Mon, Aug 10, 2026 at 11:30:03AM +0100, Frediano Ziglio wrote:
> Edwin Török (3):
>   libs/call: cache up to 4 pages in hypercall bounce buffers
>   libs/guest: allocate various migration arrays just once
> Frediano Ziglio (6):
>   libs/guest: move batch_pfns into a separate structure

I've committed these first three patches.

I've notice that `git am` will put the wrong author on your patch, it
would use the gmail addr instead of the citrix one. Could you fix your
config so that `git` does the right thing? I think it is just a matter
of changing the config:

    git config sendemail.from 'Frediano Ziglio <freddy77@gmail.com>'

(with maybe --global or with an identity added to the config option if
you use that).

This will tell git that the email is send from a different email
address and it will format the patch appropriately. Otherwise, gmail
just overwrite the "From:" without telling git. The original "From:" is
still available in "X-Google-Original-From:" but it's not something git
should care about.

Cheers,


-- 
Anthony Perard | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech

On Tue, 11 Aug 2026 at 12:37, Anthony PERARD <anthony.perard@vates.tech> wrote:
>
> On Mon, Aug 10, 2026 at 11:30:03AM +0100, Frediano Ziglio wrote:
> > Edwin Török (3):
> >   libs/call: cache up to 4 pages in hypercall bounce buffers
> >   libs/guest: allocate various migration arrays just once
> > Frediano Ziglio (6):
> >   libs/guest: move batch_pfns into a separate structure
>
> I've committed these first three patches.
>

Thanks.

> I've notice that `git am` will put the wrong author on your patch, it
> would use the gmail addr instead of the citrix one. Could you fix your
> config so that `git` does the right thing? I think it is just a matter
> of changing the config:
>
>     git config sendemail.from 'Frediano Ziglio <freddy77@gmail.com>'
>
> (with maybe --global or with an identity added to the config option if
> you use that).
>
> This will tell git that the email is send from a different email
> address and it will format the patch appropriately. Otherwise, gmail
> just overwrite the "From:" without telling git. The original "From:" is
> still available in "X-Google-Original-From:" but it's not something git
> should care about.
>

Done. Yes, it looks like it is working. An additional "From; xxx" line
is added at the beginning of the body.

> Cheers,
>
>

Frediano