mm: convert do_brk_flags() to use vma_flags_t

In order to be able to do this, we need to change VM_DATA_DEFAULT_FLAGS
and friends and update the architecture-specific definitions also.

We then have to update some KSM logic to handle VMA flags, and introduce
VMA_STACK_FLAGS to define the vma_flags_t equivalent of VM_STACK_FLAGS.

We also introduce two helper functions for use during the time we are
converting legacy flags to vma_flags_t values - vma_flags_to_legacy() and
legacy_to_vma_flags().

This enables us to iteratively make changes to break these changes up into
separate parts.

We use these explicitly here to keep VM_STACK_FLAGS around for certain
users which need to maintain the legacy vm_flags_t values for the time
being.

We are no longer able to rely on the simple VM_xxx being set to zero if
the feature is not enabled, so in the case of VM_DROPPABLE we introduce
VMA_DROPPABLE as the vma_flags_t equivalent, which is set to
EMPTY_VMA_FLAGS if the droppable flag is not available.

While we're here, we make the description of do_brk_flags() into a kdoc
comment, as it almost was already.

We use vma_flags_to_legacy() to not need to update the vm_get_page_prot()
logic as this time.

Note that in create_init_stack_vma() we have to replace the BUILD_BUG_ON()
with a VM_WARN_ON_ONCE() as the tested values are no longer build time
available.

We also update mprotect_fixup() to use VMA flags where possible, though we
have to live with a little duplication between vm_flags_t and vma_flags_t
values for the time being until further conversions are made.

While we're here, update VM_SPECIAL to be defined in terms of
VMA_SPECIAL_FLAGS now we have vma_flags_to_legacy().

Finally, we update the VMA tests to reflect these changes.

Link: https://lkml.kernel.org/r/d02e3e45d9a33d7904b149f5604904089fd640ae.1774034900.git.ljs@kernel.org
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Acked-by: Paul Moore <paul@paul-moore.com> [SELinux]
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Kees Cook <kees@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Ondrej Mosnacek <omosnace@redhat.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Richard Weinberger <richard@nod.at>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Stephen Smalley <stephen.smalley.work@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vineet Gupta <vgupta@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Will Deacon <will@kernel.org>
Cc: xu xin <xu.xin16@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>