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Commit 29eb7782 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Linus Torvalds
Browse files

arch, mm: Remove tlb_fast_mode() 



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: default avatarMax Filippov <jcmvbkbc@gmail.com>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2c95523c

arch/arm/include/asm/tlb.h

+4 −23
Original line number Diff line number Diff line
@@ -33,18 +33,6 @@ 
#include <asm/pgalloc.h>

#include <asm/tlbflush.h>



/*

 * We need to delay page freeing for SMP as other CPUs can access pages

 * which have been removed but not yet had their TLB entries invalidated.

 * Also, as ARMv7 speculative prefetch can drag new entries into the TLB,

 * we need to apply this same delaying tactic to ensure correct operation.

 */

#if defined(CONFIG_SMP) || defined(CONFIG_CPU_32v7)

#define tlb_fast_mode(tlb)	0

#else

#define tlb_fast_mode(tlb)	1

#endif



#define MMU_GATHER_BUNDLE	8



/*
@@ -112,13 +100,11 @@ static inline void __tlb_alloc_page(struct mmu_gather *tlb) 
static inline void tlb_flush_mmu(struct mmu_gather *tlb)

{

	tlb_flush(tlb);

	if (!tlb_fast_mode(tlb)) {

	free_pages_and_swap_cache(tlb->pages, tlb->nr);

	tlb->nr = 0;

	if (tlb->pages == tlb->local)

		__tlb_alloc_page(tlb);

}

}



static inline void

tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, unsigned int fullmm)
@@ -178,11 +164,6 @@ tlb_end_vma(struct mmu_gather *tlb, struct vm_area_struct *vma) 


static inline int __tlb_remove_page(struct mmu_gather *tlb, struct page *page)

{

	if (tlb_fast_mode(tlb)) {

		free_page_and_swap_cache(page);

		return 1; /* avoid calling tlb_flush_mmu */

	}



	tlb->pages[tlb->nr++] = page;

	VM_BUG_ON(tlb->nr > tlb->max);

	return tlb->max - tlb->nr;

arch/ia64/include/asm/tlb.h

+8 −33
Original line number Diff line number Diff line
@@ -46,12 +46,6 @@ 
#include <asm/tlbflush.h>

#include <asm/machvec.h>



#ifdef CONFIG_SMP

# define tlb_fast_mode(tlb)	((tlb)->nr == ~0U)

#else

# define tlb_fast_mode(tlb)	(1)

#endif



/*

 * If we can't allocate a page to make a big batch of page pointers

 * to work on, then just handle a few from the on-stack structure.
@@ -60,7 +54,7 @@ 


struct mmu_gather {

	struct mm_struct	*mm;

	unsigned int		nr;		/* == ~0U => fast mode */

	unsigned int		nr;

	unsigned int		max;

	unsigned char		fullmm;		/* non-zero means full mm flush */

	unsigned char		need_flush;	/* really unmapped some PTEs? */
@@ -103,6 +97,7 @@ extern struct ia64_tr_entry *ia64_idtrs[NR_CPUS]; 
static inline void

ia64_tlb_flush_mmu (struct mmu_gather *tlb, unsigned long start, unsigned long end)

{

	unsigned long i;

	unsigned int nr;



	if (!tlb->need_flush)
@@ -141,14 +136,12 @@ ia64_tlb_flush_mmu (struct mmu_gather *tlb, unsigned long start, unsigned long e 


	/* lastly, release the freed pages */

	nr = tlb->nr;

	if (!tlb_fast_mode(tlb)) {

		unsigned long i;



	tlb->nr = 0;

	tlb->start_addr = ~0UL;

	for (i = 0; i < nr; ++i)

		free_page_and_swap_cache(tlb->pages[i]);

}

}



static inline void __tlb_alloc_page(struct mmu_gather *tlb)

{
@@ -167,20 +160,7 @@ tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, unsigned int full_m 
	tlb->mm = mm;

	tlb->max = ARRAY_SIZE(tlb->local);

	tlb->pages = tlb->local;

	/*

	 * Use fast mode if only 1 CPU is online.

	 *

	 * It would be tempting to turn on fast-mode for full_mm_flush as well.  But this

	 * doesn't work because of speculative accesses and software prefetching: the page

	 * table of "mm" may (and usually is) the currently active page table and even

	 * though the kernel won't do any user-space accesses during the TLB shoot down, a

	 * compiler might use speculation or lfetch.fault on what happens to be a valid

	 * user-space address.  This in turn could trigger a TLB miss fault (or a VHPT

	 * walk) and re-insert a TLB entry we just removed.  Slow mode avoids such

	 * problems.  (We could make fast-mode work by switching the current task to a

	 * different "mm" during the shootdown.) --davidm 08/02/2002

	 */

	tlb->nr = (num_online_cpus() == 1) ? ~0U : 0;

	tlb->nr = 0;

	tlb->fullmm = full_mm_flush;

	tlb->start_addr = ~0UL;

}
@@ -214,11 +194,6 @@ static inline int __tlb_remove_page(struct mmu_gather *tlb, struct page *page) 
{

	tlb->need_flush = 1;



	if (tlb_fast_mode(tlb)) {

		free_page_and_swap_cache(page);

		return 1; /* avoid calling tlb_flush_mmu */

	}



	if (!tlb->nr && tlb->pages == tlb->local)

		__tlb_alloc_page(tlb);

include/asm-generic/tlb.h

+1 −16
Original line number Diff line number Diff line
@@ -97,11 +97,9 @@ struct mmu_gather { 
	unsigned long		start;

	unsigned long		end;

	unsigned int		need_flush : 1,	/* Did free PTEs */

				fast_mode  : 1; /* No batching   */



	/* we are in the middle of an operation to clear

	 * a full mm and can make some optimizations */

	unsigned int		fullmm : 1,

				fullmm : 1,

	/* we have performed an operation which

	 * requires a complete flush of the tlb */

				need_flush_all : 1;
@@ -114,19 +112,6 @@ struct mmu_gather { 


#define HAVE_GENERIC_MMU_GATHER



static inline int tlb_fast_mode(struct mmu_gather *tlb)

{

#ifdef CONFIG_SMP

	return tlb->fast_mode;

#else

	/*

	 * For UP we don't need to worry about TLB flush

	 * and page free order so much..

	 */

	return 1;

#endif

}



void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, bool fullmm);

void tlb_flush_mmu(struct mmu_gather *tlb);

void tlb_finish_mmu(struct mmu_gather *tlb, unsigned long start,

mm/memory.c

+0 −9
Original line number Diff line number Diff line
@@ -220,7 +220,6 @@ void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, bool fullmm) 
	tlb->start	= -1UL;

	tlb->end	= 0;

	tlb->need_flush = 0;

	tlb->fast_mode  = (num_possible_cpus() == 1);

	tlb->local.next = NULL;

	tlb->local.nr   = 0;

	tlb->local.max  = ARRAY_SIZE(tlb->__pages);
@@ -244,9 +243,6 @@ void tlb_flush_mmu(struct mmu_gather *tlb) 
	tlb_table_flush(tlb);

#endif



	if (tlb_fast_mode(tlb))

		return;



	for (batch = &tlb->local; batch; batch = batch->next) {

		free_pages_and_swap_cache(batch->pages, batch->nr);

		batch->nr = 0;
@@ -288,11 +284,6 @@ int __tlb_remove_page(struct mmu_gather *tlb, struct page *page) 


	VM_BUG_ON(!tlb->need_flush);



	if (tlb_fast_mode(tlb)) {

		free_page_and_swap_cache(page);

		return 1; /* avoid calling tlb_flush_mmu() */

	}



	batch = tlb->active;

	batch->pages[batch->nr++] = page;

	if (batch->nr == batch->max) {