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https://github.com/torvalds/linux
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5e31275cc9
Introduce per-VMA locking. The lock implementation relies on a per-vma
and per-mm sequence counters to note exclusive locking:
- read lock - (implemented by vma_start_read) requires the vma
(vm_lock_seq) and mm (mm_lock_seq) sequence counters to differ.
If they match then there must be a vma exclusive lock held somewhere.
- read unlock - (implemented by vma_end_read) is a trivial vma->lock
unlock.
- write lock - (vma_start_write) requires the mmap_lock to be held
exclusively and the current mm counter is assigned to the vma counter.
This will allow multiple vmas to be locked under a single mmap_lock
write lock (e.g. during vma merging). The vma counter is modified
under exclusive vma lock.
- write unlock - (vma_end_write_all) is a batch release of all vma
locks held. It doesn't pair with a specific vma_start_write! It is
done before exclusive mmap_lock is released by incrementing mm
sequence counter (mm_lock_seq).
- write downgrade - if the mmap_lock is downgraded to the read lock, all
vma write locks are released as well (effectivelly same as write
unlock).
Link: https://lkml.kernel.org/r/20230227173632.3292573-13-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
59 lines
1.7 KiB
C
59 lines
1.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/mm_types.h>
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#include <linux/maple_tree.h>
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#include <linux/rwsem.h>
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#include <linux/spinlock.h>
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#include <linux/list.h>
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#include <linux/cpumask.h>
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#include <linux/mman.h>
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#include <linux/pgtable.h>
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#include <linux/atomic.h>
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#include <linux/user_namespace.h>
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#include <linux/ioasid.h>
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#include <asm/mmu.h>
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#ifndef INIT_MM_CONTEXT
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#define INIT_MM_CONTEXT(name)
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#endif
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/*
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* For dynamically allocated mm_structs, there is a dynamically sized cpumask
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* at the end of the structure, the size of which depends on the maximum CPU
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* number the system can see. That way we allocate only as much memory for
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* mm_cpumask() as needed for the hundreds, or thousands of processes that
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* a system typically runs.
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*
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* Since there is only one init_mm in the entire system, keep it simple
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* and size this cpu_bitmask to NR_CPUS.
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*/
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struct mm_struct init_mm = {
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.mm_mt = MTREE_INIT_EXT(mm_mt, MM_MT_FLAGS, init_mm.mmap_lock),
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.pgd = swapper_pg_dir,
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.mm_users = ATOMIC_INIT(2),
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.mm_count = ATOMIC_INIT(1),
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.write_protect_seq = SEQCNT_ZERO(init_mm.write_protect_seq),
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MMAP_LOCK_INITIALIZER(init_mm)
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.page_table_lock = __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock),
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.arg_lock = __SPIN_LOCK_UNLOCKED(init_mm.arg_lock),
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.mmlist = LIST_HEAD_INIT(init_mm.mmlist),
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#ifdef CONFIG_PER_VMA_LOCK
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.mm_lock_seq = 0,
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#endif
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.user_ns = &init_user_ns,
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.cpu_bitmap = CPU_BITS_NONE,
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#ifdef CONFIG_IOMMU_SVA
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.pasid = INVALID_IOASID,
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#endif
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INIT_MM_CONTEXT(init_mm)
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};
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void setup_initial_init_mm(void *start_code, void *end_code,
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void *end_data, void *brk)
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{
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init_mm.start_code = (unsigned long)start_code;
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init_mm.end_code = (unsigned long)end_code;
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init_mm.end_data = (unsigned long)end_data;
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init_mm.brk = (unsigned long)brk;
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}
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