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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/20200116064531.483522-10-aneesh.kumar@linux.ibm.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Peter Zijlstra 2020-02-03 17:37:11 -08:00 committed by Linus Torvalds
parent 580a586c40
commit 0d6e24d430
4 changed files with 132 additions and 73 deletions
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5
arch/Kconfig
View File

@ -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
@ -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

4
arch/arm/include/asm/tlb.h
View File

@ -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)
{

72
include/asm-generic/tlb.h
View File

@ -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()
*
@ -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().
@ -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];
};
@ -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.
@ -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

124
mm/mmu_gather.c
View File

@ -91,12 +91,87 @@ bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, int page_
#endif /* MMU_GATHER_NO_GATHER */
#ifdef CONFIG_MMU_GATHER_TABLE_FREE
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
/*
* See the comment near struct mmu_table_batch.
* 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 void tlb_remove_table_smp_sync(void *arg)
{
/* Simply deliver the interrupt */
}
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.
*/
smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
}
static void tlb_remove_table_rcu(struct rcu_head *head)
{
__tlb_remove_table_free(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);
}
#else /* !CONFIG_MMU_GATHER_RCU_TABLE_FREE */
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.
*/
@ -112,44 +187,19 @@ static inline void tlb_table_invalidate(struct mmu_gather *tlb)
}
}
static void tlb_remove_table_smp_sync(void *arg)
{
/* Simply deliver the interrupt */
}
static void tlb_remove_table_one(void *table)
{
/*
* 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.
*/
smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
tlb_remove_table_sync_one();
__tlb_remove_table(table);
}
static void tlb_remove_table_rcu(struct rcu_head *head)
{
struct mmu_table_batch *batch;
int i;
batch = container_of(head, struct mmu_table_batch, rcu);
for (i = 0; i < batch->nr; i++)
__tlb_remove_table(batch->tables[i]);
free_page((unsigned long)batch);
}
static void tlb_table_flush(struct mmu_gather *tlb)
{
struct mmu_table_batch **batch = &tlb->batch;
if (*batch) {
tlb_table_invalidate(tlb);
call_rcu(&(*batch)->rcu, tlb_remove_table_rcu);
tlb_remove_table_free(*batch);
*batch = NULL;
}
}
@ -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
@ -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