Re: [PATCH RFC 0/5] mm/gup: Introduce exclusive GUP pinning

[Elliot Berman <quic_eberman@quicinc.com>]

b4 wasn't happy with my copy/paste of the CC list from Fuad's series
[1]. CC'ing them here.

[1]: https://lore.kernel.org/all/20240222161047.402609-1-tabba@google.com/

On Tue, Jun 18, 2024 at 05:05:06PM -0700, Elliot Berman wrote:
> In arm64 pKVM and QuIC's Gunyah protected VM model, we want to support
> grabbing shmem user pages instead of using KVM's guestmemfd. These
> hypervisors provide a different isolation model than the CoCo
> implementations from x86. KVM's guest_memfd is focused on providing
> memory that is more isolated than AVF requires. Some specific examples
> include ability to pre-load data onto guest-private pages, dynamically
> sharing/isolating guest pages without copy, and (future) migrating
> guest-private pages.  In sum of those differences after a discussion in
> [1] and at PUCK, we want to try to stick with existing shmem and extend
> GUP to support the isolation needs for arm64 pKVM and Gunyah. To that
> end, we introduce the concept of "exclusive GUP pinning", which enforces
> that only one pin of any kind is allowed when using the FOLL_EXCLUSIVE
> flag is set. This behavior doesn't affect FOLL_GET or any other folio
> refcount operations that don't go through the FOLL_PIN path.
> 
> [1]: https://lore.kernel.org/all/20240319143119.GA2736@willie-the-truck/
> 
> Tree with patches at:
> https://git.codelinaro.org/clo/linux-kernel/gunyah-linux/-/tree/sent/exclusive-gup-v1
> 
> 
> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
> ---
> Elliot Berman (2):
>       mm/gup-test: Verify exclusive pinned
>       mm/gup_test: Verify GUP grabs same pages twice
> 
> Fuad Tabba (3):
>       mm/gup: Move GUP_PIN_COUNTING_BIAS to page_ref.h
>       mm/gup: Add an option for obtaining an exclusive pin
>       mm/gup: Add support for re-pinning a normal pinned page as exclusive
> 
>  include/linux/mm.h                    |  57 ++++----
>  include/linux/mm_types.h              |   2 +
>  include/linux/page_ref.h              |  74 ++++++++++
>  mm/Kconfig                            |   5 +
>  mm/gup.c                              | 265 ++++++++++++++++++++++++++++++----
>  mm/gup_test.c                         | 108 ++++++++++++++
>  mm/gup_test.h                         |   1 +
>  tools/testing/selftests/mm/gup_test.c |   5 +-
>  8 files changed, 457 insertions(+), 60 deletions(-)
> ---
> base-commit: 6ba59ff4227927d3a8530fc2973b80e94b54d58f
> change-id: 20240509-exclusive-gup-66259138bbff
> 
> Best regards,
> -- 
> Elliot Berman <quic_eberman@quicinc.com>
>