![Peter Zijlstra](/assets/img/avatar_default.png)
Since the introduction of preemptible mmu_gather TLB fast mode has been broken. TLB fast mode relies on there being absolutely no concurrency; it frees pages first and invalidates TLBs later. However now we can get concurrency and stuff goes *bang*. This patch removes all tlb_fast_mode() code; it was found the better option vs trying to patch the hole by entangling tlb invalidation with the scheduler. Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Russell King <linux@arm.linux.org.uk> Cc: Tony Luck <tony.luck@intel.com> Reported-by: Max Filippov <jcmvbkbc@gmail.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
181 lines
5.5 KiB
C
181 lines
5.5 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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unsigned int need_flush : 1, /* Did free PTEs */
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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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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, bool fullmm);
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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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/**
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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 umapped in ->need_flush, so we can
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* later optimise away the tlb invalidate. This helps when userspace is
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* 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->need_flush = 1; \
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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->need_flush = 1; \
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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->need_flush = 1; \
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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->need_flush = 1; \
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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->need_flush = 1; \
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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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