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7a9cdebdcc
Jann Horn points out that the vmacache_flush_all() function is not only potentially expensive, it's buggy too. It also happens to be entirely unnecessary, because the sequence number overflow case can be avoided by simply making the sequence number be 64-bit. That doesn't even grow the data structures in question, because the other adjacent fields are already 64-bit. So simplify the whole thing by just making the sequence number overflow case go away entirely, which gets rid of all the complications and makes the code faster too. Win-win. [ Oleg Nesterov points out that the VMACACHE_FULL_FLUSHES statistics also just goes away entirely with this ] Reported-by: Jann Horn <jannh@google.com> Suggested-by: Will Deacon <will.deacon@arm.com> Acked-by: Davidlohr Bueso <dave@stgolabs.net> Cc: Oleg Nesterov <oleg@redhat.com> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
119 lines
2.7 KiB
C
119 lines
2.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2014 Davidlohr Bueso.
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*/
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#include <linux/sched/signal.h>
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#include <linux/sched/task.h>
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#include <linux/mm.h>
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#include <linux/vmacache.h>
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#include <asm/pgtable.h>
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/*
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* Hash based on the pmd of addr if configured with MMU, which provides a good
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* hit rate for workloads with spatial locality. Otherwise, use pages.
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*/
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#ifdef CONFIG_MMU
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#define VMACACHE_SHIFT PMD_SHIFT
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#else
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#define VMACACHE_SHIFT PAGE_SHIFT
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#endif
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#define VMACACHE_HASH(addr) ((addr >> VMACACHE_SHIFT) & VMACACHE_MASK)
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/*
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* This task may be accessing a foreign mm via (for example)
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* get_user_pages()->find_vma(). The vmacache is task-local and this
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* task's vmacache pertains to a different mm (ie, its own). There is
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* nothing we can do here.
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*
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* Also handle the case where a kernel thread has adopted this mm via use_mm().
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* That kernel thread's vmacache is not applicable to this mm.
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*/
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static inline bool vmacache_valid_mm(struct mm_struct *mm)
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{
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return current->mm == mm && !(current->flags & PF_KTHREAD);
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}
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void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
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{
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if (vmacache_valid_mm(newvma->vm_mm))
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current->vmacache.vmas[VMACACHE_HASH(addr)] = newvma;
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}
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static bool vmacache_valid(struct mm_struct *mm)
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{
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struct task_struct *curr;
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if (!vmacache_valid_mm(mm))
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return false;
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curr = current;
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if (mm->vmacache_seqnum != curr->vmacache.seqnum) {
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/*
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* First attempt will always be invalid, initialize
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* the new cache for this task here.
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*/
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curr->vmacache.seqnum = mm->vmacache_seqnum;
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vmacache_flush(curr);
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return false;
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}
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return true;
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}
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struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
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{
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int idx = VMACACHE_HASH(addr);
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int i;
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count_vm_vmacache_event(VMACACHE_FIND_CALLS);
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if (!vmacache_valid(mm))
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return NULL;
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for (i = 0; i < VMACACHE_SIZE; i++) {
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struct vm_area_struct *vma = current->vmacache.vmas[idx];
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if (vma) {
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#ifdef CONFIG_DEBUG_VM_VMACACHE
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if (WARN_ON_ONCE(vma->vm_mm != mm))
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break;
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#endif
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if (vma->vm_start <= addr && vma->vm_end > addr) {
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count_vm_vmacache_event(VMACACHE_FIND_HITS);
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return vma;
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}
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}
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if (++idx == VMACACHE_SIZE)
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idx = 0;
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}
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return NULL;
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}
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#ifndef CONFIG_MMU
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struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
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unsigned long start,
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unsigned long end)
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{
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int idx = VMACACHE_HASH(start);
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int i;
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count_vm_vmacache_event(VMACACHE_FIND_CALLS);
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if (!vmacache_valid(mm))
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return NULL;
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for (i = 0; i < VMACACHE_SIZE; i++) {
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struct vm_area_struct *vma = current->vmacache.vmas[idx];
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if (vma && vma->vm_start == start && vma->vm_end == end) {
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count_vm_vmacache_event(VMACACHE_FIND_HITS);
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return vma;
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}
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if (++idx == VMACACHE_SIZE)
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idx = 0;
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}
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return NULL;
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}
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#endif
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