[RFC] mm/gup: Introduce exclusive GUP pinning

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

To: Andrew Morton <akpm@linux-foundation.org>
To: Shuah Khan <shuah@kernel.org>
To: David Hildenbrand <david@redhat.com>
To: Matthew Wilcox <willy@infradead.org>
To: maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, seanjc@google.com, Vishal Annapurve <vannapurve@google.com>, Fuad Tabba <tabba@google.com>
Cc: kvm@vger.kernel.org, kvmarm@lists.linux.dev
Cc: linux-arm-msm@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org
Cc: pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au,
	 anup@brainfault.org, paul.walmsley@sifive.com,
	palmer@dabbelt.com,  aou@eecs.berkeley.edu, seanjc@google.com,
	viro@zeniv.linux.org.uk,  brauner@kernel.org,
	willy@infradead.org, akpm@linux-foundation.org,
	 xiaoyao.li@intel.com, yilun.xu@intel.com,
	chao.p.peng@linux.intel.com,  jarkko@kernel.org,
	amoorthy@google.com, dmatlack@google.com,
	 yu.c.zhang@linux.intel.com, isaku.yamahata@intel.com,
	mic@digikod.net,  vbabka@suse.cz, vannapurve@google.com,
	ackerleytng@google.com,  mail@maciej.szmigiero.name,
	david@redhat.com, michael.roth@amd.com,  wei.w.wang@intel.com,
	liam.merwick@oracle.com, isaku.yamahata@gmail.com,
	 kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com,
	steven.price@arm.com,  quic_eberman@quicinc.com,
	quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com,
	 quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com,
	 quic_pderrin@quicinc.com, quic_pheragu@quicinc.com,
	catalin.marinas@arm.com,  james.morse@arm.com,
	yuzenghui@huawei.com, oliver.upton@linux.dev,  maz@kernel.org,
	will@kernel.org, qperret@google.com, keirf@google.com,
	 tabba@google.com
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,

Linux 6.9