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![Will Deacon](/assets/img/avatar_default.png)
When batching up address ranges for TLB invalidation, we check tlb->end != 0 to indicate that some pages have actually been unmapped. As of commitf045bbb9fa
("mmu_gather: fix over-eager tlb_flush_mmu_free() calling"), we use the same check for freeing these pages in order to avoid a performance regression where we call free_pages_and_swap_cache even when no pages are actually queued up. Unfortunately, the range could have been reset (tlb->end = 0) by tlb_end_vma, which has been shown to cause memory leaks on arm64. Furthermore, investigation into these leaks revealed that the fullmm case on task exit no longer invalidates the TLB, by virtue of tlb->end == 0 (in 3.18, need_flush would have been set). This patch resolves the problem by reverting commitf045bbb9fa
, using instead tlb->local.nr as the predicate for page freeing in tlb_flush_mmu_free and ensuring that tlb->end is initialised to a non-zero value in the fullmm case. Tested-by: Mark Langsdorf <mlangsdo@redhat.com> Tested-by: Dave Hansen <dave@sr71.net> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
221 lines
6.5 KiB
C
221 lines
6.5 KiB
C
/* include/asm-generic/tlb.h
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*
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* Generic TLB shootdown code
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*
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* Copyright 2001 Red Hat, Inc.
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* Based on code from mm/memory.c Copyright Linus Torvalds and others.
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*
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* Copyright 2011 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#ifndef _ASM_GENERIC__TLB_H
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#define _ASM_GENERIC__TLB_H
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#include <linux/swap.h>
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#include <asm/pgalloc.h>
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#include <asm/tlbflush.h>
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#ifdef CONFIG_HAVE_RCU_TABLE_FREE
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/*
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* Semi RCU freeing of the page directories.
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*
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* This is needed by some architectures to implement software pagetable walkers.
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*
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* gup_fast() and other software pagetable walkers do a lockless page-table
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* walk and therefore needs some synchronization with the freeing of the page
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* directories. The chosen means to accomplish that is by disabling IRQs over
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* the walk.
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*
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* Architectures that use IPIs to flush TLBs will then automagically DTRT,
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* since we unlink the page, flush TLBs, free the page. Since the disabling of
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* IRQs delays the completion of the TLB flush we can never observe an already
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* freed page.
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*
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* Architectures that do not have this (PPC) need to delay the freeing by some
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* other means, this is that means.
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*
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* What we do is batch the freed directory pages (tables) and RCU free them.
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* We use the sched RCU variant, as that guarantees that IRQ/preempt disabling
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* holds off grace periods.
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*
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* However, in order to batch these pages we need to allocate storage, this
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* allocation is deep inside the MM code and can thus easily fail on memory
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* pressure. To guarantee progress we fall back to single table freeing, see
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* the implementation of tlb_remove_table_one().
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*
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*/
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struct mmu_table_batch {
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struct rcu_head rcu;
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unsigned int nr;
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void *tables[0];
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};
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#define MAX_TABLE_BATCH \
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((PAGE_SIZE - sizeof(struct mmu_table_batch)) / sizeof(void *))
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extern void tlb_table_flush(struct mmu_gather *tlb);
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extern void tlb_remove_table(struct mmu_gather *tlb, void *table);
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#endif
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/*
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* If we can't allocate a page to make a big batch of page pointers
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* to work on, then just handle a few from the on-stack structure.
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*/
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#define MMU_GATHER_BUNDLE 8
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struct mmu_gather_batch {
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struct mmu_gather_batch *next;
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unsigned int nr;
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unsigned int max;
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struct page *pages[0];
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};
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#define MAX_GATHER_BATCH \
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((PAGE_SIZE - sizeof(struct mmu_gather_batch)) / sizeof(void *))
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/*
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* Limit the maximum number of mmu_gather batches to reduce a risk of soft
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* lockups for non-preemptible kernels on huge machines when a lot of memory
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* is zapped during unmapping.
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* 10K pages freed at once should be safe even without a preemption point.
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*/
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#define MAX_GATHER_BATCH_COUNT (10000UL/MAX_GATHER_BATCH)
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/* struct mmu_gather is an opaque type used by the mm code for passing around
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* any data needed by arch specific code for tlb_remove_page.
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*/
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struct mmu_gather {
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struct mm_struct *mm;
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#ifdef CONFIG_HAVE_RCU_TABLE_FREE
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struct mmu_table_batch *batch;
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#endif
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unsigned long start;
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unsigned long end;
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/* we are in the middle of an operation to clear
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* a full mm and can make some optimizations */
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unsigned int fullmm : 1,
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/* we have performed an operation which
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* requires a complete flush of the tlb */
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need_flush_all : 1;
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struct mmu_gather_batch *active;
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struct mmu_gather_batch local;
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struct page *__pages[MMU_GATHER_BUNDLE];
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unsigned int batch_count;
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};
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#define HAVE_GENERIC_MMU_GATHER
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void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, unsigned long start, unsigned long end);
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void tlb_flush_mmu(struct mmu_gather *tlb);
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void tlb_finish_mmu(struct mmu_gather *tlb, unsigned long start,
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unsigned long end);
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int __tlb_remove_page(struct mmu_gather *tlb, struct page *page);
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/* tlb_remove_page
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* Similar to __tlb_remove_page but will call tlb_flush_mmu() itself when
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* required.
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*/
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static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
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{
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if (!__tlb_remove_page(tlb, page))
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tlb_flush_mmu(tlb);
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}
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static inline void __tlb_adjust_range(struct mmu_gather *tlb,
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unsigned long address)
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{
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tlb->start = min(tlb->start, address);
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tlb->end = max(tlb->end, address + PAGE_SIZE);
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}
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static inline void __tlb_reset_range(struct mmu_gather *tlb)
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{
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if (tlb->fullmm) {
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tlb->start = tlb->end = ~0;
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} else {
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tlb->start = TASK_SIZE;
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tlb->end = 0;
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}
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}
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/*
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* In the case of tlb vma handling, we can optimise these away in the
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* case where we're doing a full MM flush. When we're doing a munmap,
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* the vmas are adjusted to only cover the region to be torn down.
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*/
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#ifndef tlb_start_vma
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#define tlb_start_vma(tlb, vma) do { } while (0)
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#endif
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#define __tlb_end_vma(tlb, vma) \
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do { \
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if (!tlb->fullmm && tlb->end) { \
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tlb_flush(tlb); \
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__tlb_reset_range(tlb); \
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} \
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} while (0)
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#ifndef tlb_end_vma
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#define tlb_end_vma __tlb_end_vma
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#endif
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#ifndef __tlb_remove_tlb_entry
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#define __tlb_remove_tlb_entry(tlb, ptep, address) do { } while (0)
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#endif
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/**
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* tlb_remove_tlb_entry - remember a pte unmapping for later tlb invalidation.
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*
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* Record the fact that pte's were really unmapped by updating the range,
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* so we can later optimise away the tlb invalidate. This helps when
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* userspace is unmapping already-unmapped pages, which happens quite a lot.
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*/
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#define tlb_remove_tlb_entry(tlb, ptep, address) \
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do { \
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__tlb_adjust_range(tlb, address); \
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__tlb_remove_tlb_entry(tlb, ptep, address); \
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} while (0)
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/**
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* tlb_remove_pmd_tlb_entry - remember a pmd mapping for later tlb invalidation
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* This is a nop so far, because only x86 needs it.
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*/
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#ifndef __tlb_remove_pmd_tlb_entry
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#define __tlb_remove_pmd_tlb_entry(tlb, pmdp, address) do {} while (0)
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#endif
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#define tlb_remove_pmd_tlb_entry(tlb, pmdp, address) \
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do { \
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__tlb_adjust_range(tlb, address); \
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__tlb_remove_pmd_tlb_entry(tlb, pmdp, address); \
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} while (0)
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#define pte_free_tlb(tlb, ptep, address) \
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do { \
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__tlb_adjust_range(tlb, address); \
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__pte_free_tlb(tlb, ptep, address); \
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} while (0)
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#ifndef __ARCH_HAS_4LEVEL_HACK
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#define pud_free_tlb(tlb, pudp, address) \
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do { \
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__tlb_adjust_range(tlb, address); \
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__pud_free_tlb(tlb, pudp, address); \
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} while (0)
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#endif
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#define pmd_free_tlb(tlb, pmdp, address) \
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do { \
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__tlb_adjust_range(tlb, address); \
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__pmd_free_tlb(tlb, pmdp, address); \
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} while (0)
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#define tlb_migrate_finish(mm) do {} while (0)
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#endif /* _ASM_GENERIC__TLB_H */
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