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asm-generic/tlb: provide MMU_GATHER_TABLE_FREE
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As described in the comment, the correct order for freeing pages is:

 1) unhook page
 2) TLB invalidate page
 3) free page

This order equally applies to page directories.

Currently there are two correct options:

 - use tlb_remove_page(), when all page directores are full pages and
   there are no futher contraints placed by things like software
   walkers (HAVE_FAST_GUP).

 - use MMU_GATHER_RCU_TABLE_FREE and tlb_remove_table() when the
   architecture does not do IPI based TLB invalidate and has
   HAVE_FAST_GUP (or software TLB fill).

This however leaves architectures that don't have page based directories
but don't need RCU in a bind.  For those, provide MMU_GATHER_TABLE_FREE,
which provides the independent batching for directories without the
additional RCU freeing.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Aneesh Kumar K.V <[email protected]>
Cc: Michael Ellerman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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Peter Zijlstra authored and torvalds committed Feb 4, 2020
1 parent 580a586 commit 0d6e24d
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Showing 4 changed files with 130 additions and 71 deletions.
5 changes: 5 additions & 0 deletions arch/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -393,8 +393,12 @@ config HAVE_ARCH_JUMP_LABEL
config HAVE_ARCH_JUMP_LABEL_RELATIVE
bool

config MMU_GATHER_TABLE_FREE
bool

config MMU_GATHER_RCU_TABLE_FREE
bool
select MMU_GATHER_TABLE_FREE

config MMU_GATHER_PAGE_SIZE
bool
Expand All @@ -404,6 +408,7 @@ config MMU_GATHER_NO_RANGE

config MMU_GATHER_NO_GATHER
bool
depends on MMU_GATHER_TABLE_FREE

config ARCH_HAVE_NMI_SAFE_CMPXCHG
bool
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4 changes: 0 additions & 4 deletions arch/arm/include/asm/tlb.h
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Original file line number Diff line number Diff line change
Expand Up @@ -37,10 +37,6 @@ static inline void __tlb_remove_table(void *_table)

#include <asm-generic/tlb.h>

#ifndef CONFIG_MMU_GATHER_RCU_TABLE_FREE
#define tlb_remove_table(tlb, entry) tlb_remove_page(tlb, entry)
#endif

static inline void
__pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte, unsigned long addr)
{
Expand Down
72 changes: 37 additions & 35 deletions include/asm-generic/tlb.h
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,15 @@
* Defaults to flushing at tlb_end_vma() to reset the range; helps when
* there's large holes between the VMAs.
*
* - tlb_remove_table()
*
* tlb_remove_table() is the basic primitive to free page-table directories
* (__p*_free_tlb()). In it's most primitive form it is an alias for
* tlb_remove_page() below, for when page directories are pages and have no
* additional constraints.
*
* See also MMU_GATHER_TABLE_FREE and MMU_GATHER_RCU_TABLE_FREE.
*
* - tlb_remove_page() / __tlb_remove_page()
* - tlb_remove_page_size() / __tlb_remove_page_size()
*
Expand Down Expand Up @@ -129,17 +138,24 @@
* This might be useful if your architecture has size specific TLB
* invalidation instructions.
*
* MMU_GATHER_RCU_TABLE_FREE
* MMU_GATHER_TABLE_FREE
*
* This provides tlb_remove_table(), to be used instead of tlb_remove_page()
* for page directores (__p*_free_tlb()). This provides separate freeing of
* the page-table pages themselves in a semi-RCU fashion (see comment below).
* Useful if your architecture doesn't use IPIs for remote TLB invalidates
* and therefore doesn't naturally serialize with software page-table walkers.
* for page directores (__p*_free_tlb()).
*
* Useful if your architecture has non-page page directories.
*
* When used, an architecture is expected to provide __tlb_remove_table()
* which does the actual freeing of these pages.
*
* MMU_GATHER_RCU_TABLE_FREE
*
* Like MMU_GATHER_TABLE_FREE, and adds semi-RCU semantics to the free (see
* comment below).
*
* Useful if your architecture doesn't use IPIs for remote TLB invalidates
* and therefore doesn't naturally serialize with software page-table walkers.
*
* MMU_GATHER_NO_RANGE
*
* Use this if your architecture lacks an efficient flush_tlb_range().
Expand All @@ -155,37 +171,12 @@
* various ptep_get_and_clear() functions.
*/

#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
/*
* Semi RCU freeing of the page directories.
*
* This is needed by some architectures to implement software pagetable walkers.
*
* gup_fast() and other software pagetable walkers do a lockless page-table
* walk and therefore needs some synchronization with the freeing of the page
* directories. The chosen means to accomplish that is by disabling IRQs over
* the walk.
*
* Architectures that use IPIs to flush TLBs will then automagically DTRT,
* since we unlink the page, flush TLBs, free the page. Since the disabling of
* IRQs delays the completion of the TLB flush we can never observe an already
* freed page.
*
* Architectures that do not have this (PPC) need to delay the freeing by some
* other means, this is that means.
*
* What we do is batch the freed directory pages (tables) and RCU free them.
* We use the sched RCU variant, as that guarantees that IRQ/preempt disabling
* holds off grace periods.
*
* However, in order to batch these pages we need to allocate storage, this
* allocation is deep inside the MM code and can thus easily fail on memory
* pressure. To guarantee progress we fall back to single table freeing, see
* the implementation of tlb_remove_table_one().
*
*/
#ifdef CONFIG_MMU_GATHER_TABLE_FREE

struct mmu_table_batch {
#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
struct rcu_head rcu;
#endif
unsigned int nr;
void *tables[0];
};
Expand All @@ -195,6 +186,17 @@ struct mmu_table_batch {

extern void tlb_remove_table(struct mmu_gather *tlb, void *table);

#else /* !CONFIG_MMU_GATHER_HAVE_TABLE_FREE */

/*
* Without MMU_GATHER_TABLE_FREE the architecture is assumed to have page based
* page directories and we can use the normal page batching to free them.
*/
#define tlb_remove_table(tlb, page) tlb_remove_page((tlb), (page))

#endif /* CONFIG_MMU_GATHER_TABLE_FREE */

#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
/*
* This allows an architecture that does not use the linux page-tables for
* hardware to skip the TLBI when freeing page tables.
Expand Down Expand Up @@ -248,7 +250,7 @@ extern bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page,
struct mmu_gather {
struct mm_struct *mm;

#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
#ifdef CONFIG_MMU_GATHER_TABLE_FREE
struct mmu_table_batch *batch;
#endif

Expand Down
120 changes: 88 additions & 32 deletions mm/mmu_gather.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -91,56 +91,106 @@ bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, int page_

#endif /* MMU_GATHER_NO_GATHER */

#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
#ifdef CONFIG_MMU_GATHER_TABLE_FREE

/*
* See the comment near struct mmu_table_batch.
*/
static void __tlb_remove_table_free(struct mmu_table_batch *batch)
{
int i;

for (i = 0; i < batch->nr; i++)
__tlb_remove_table(batch->tables[i]);

free_page((unsigned long)batch);
}

#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE

/*
* If we want tlb_remove_table() to imply TLB invalidates.
* Semi RCU freeing of the page directories.
*
* This is needed by some architectures to implement software pagetable walkers.
*
* gup_fast() and other software pagetable walkers do a lockless page-table
* walk and therefore needs some synchronization with the freeing of the page
* directories. The chosen means to accomplish that is by disabling IRQs over
* the walk.
*
* Architectures that use IPIs to flush TLBs will then automagically DTRT,
* since we unlink the page, flush TLBs, free the page. Since the disabling of
* IRQs delays the completion of the TLB flush we can never observe an already
* freed page.
*
* Architectures that do not have this (PPC) need to delay the freeing by some
* other means, this is that means.
*
* What we do is batch the freed directory pages (tables) and RCU free them.
* We use the sched RCU variant, as that guarantees that IRQ/preempt disabling
* holds off grace periods.
*
* However, in order to batch these pages we need to allocate storage, this
* allocation is deep inside the MM code and can thus easily fail on memory
* pressure. To guarantee progress we fall back to single table freeing, see
* the implementation of tlb_remove_table_one().
*
*/
static inline void tlb_table_invalidate(struct mmu_gather *tlb)
{
if (tlb_needs_table_invalidate()) {
/*
* Invalidate page-table caches used by hardware walkers. Then
* we still need to RCU-sched wait while freeing the pages
* because software walkers can still be in-flight.
*/
tlb_flush_mmu_tlbonly(tlb);
}
}

static void tlb_remove_table_smp_sync(void *arg)
{
/* Simply deliver the interrupt */
}

static void tlb_remove_table_one(void *table)
static void tlb_remove_table_sync_one(void)
{
/*
* This isn't an RCU grace period and hence the page-tables cannot be
* assumed to be actually RCU-freed.
*
* It is however sufficient for software page-table walkers that rely on
* IRQ disabling. See the comment near struct mmu_table_batch.
* IRQ disabling.
*/
smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
__tlb_remove_table(table);
}

static void tlb_remove_table_rcu(struct rcu_head *head)
{
struct mmu_table_batch *batch;
int i;
__tlb_remove_table_free(container_of(head, struct mmu_table_batch, rcu));
}

batch = container_of(head, struct mmu_table_batch, rcu);
static void tlb_remove_table_free(struct mmu_table_batch *batch)
{
call_rcu(&batch->rcu, tlb_remove_table_rcu);
}

for (i = 0; i < batch->nr; i++)
__tlb_remove_table(batch->tables[i]);
#else /* !CONFIG_MMU_GATHER_RCU_TABLE_FREE */

free_page((unsigned long)batch);
static void tlb_remove_table_sync_one(void) { }

static void tlb_remove_table_free(struct mmu_table_batch *batch)
{
__tlb_remove_table_free(batch);
}

#endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */

/*
* If we want tlb_remove_table() to imply TLB invalidates.
*/
static inline void tlb_table_invalidate(struct mmu_gather *tlb)
{
if (tlb_needs_table_invalidate()) {
/*
* Invalidate page-table caches used by hardware walkers. Then
* we still need to RCU-sched wait while freeing the pages
* because software walkers can still be in-flight.
*/
tlb_flush_mmu_tlbonly(tlb);
}
}

static void tlb_remove_table_one(void *table)
{
tlb_remove_table_sync_one();
__tlb_remove_table(table);
}

static void tlb_table_flush(struct mmu_gather *tlb)
Expand All @@ -149,7 +199,7 @@ static void tlb_table_flush(struct mmu_gather *tlb)

if (*batch) {
tlb_table_invalidate(tlb);
call_rcu(&(*batch)->rcu, tlb_remove_table_rcu);
tlb_remove_table_free(*batch);
*batch = NULL;
}
}
Expand All @@ -173,13 +223,21 @@ void tlb_remove_table(struct mmu_gather *tlb, void *table)
tlb_table_flush(tlb);
}

#endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */
static inline void tlb_table_init(struct mmu_gather *tlb)
{
tlb->batch = NULL;
}

#else /* !CONFIG_MMU_GATHER_TABLE_FREE */

static inline void tlb_table_flush(struct mmu_gather *tlb) { }
static inline void tlb_table_init(struct mmu_gather *tlb) { }

#endif /* CONFIG_MMU_GATHER_TABLE_FREE */

static void tlb_flush_mmu_free(struct mmu_gather *tlb)
{
#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
tlb_table_flush(tlb);
#endif
#ifndef CONFIG_MMU_GATHER_NO_GATHER
tlb_batch_pages_flush(tlb);
#endif
Expand Down Expand Up @@ -220,9 +278,7 @@ void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
tlb->batch_count = 0;
#endif

#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
tlb->batch = NULL;
#endif
tlb_table_init(tlb);
#ifdef CONFIG_MMU_GATHER_PAGE_SIZE
tlb->page_size = 0;
#endif
Expand Down

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