From 93274f1dd6b0a615b299beddf99871fe81f91275 Mon Sep 17 00:00:00 2001 From: Dennis Zhou Date: Sat, 3 Jul 2021 03:49:57 +0000 Subject: [PATCH] percpu: flush tlb in pcpu_reclaim_populated() Prior to "percpu: implement partial chunk depopulation", pcpu_depopulate_chunk() was called only on the destruction path. This meant the virtual address range was on its way back to vmalloc which will handle flushing the tlbs for us. However, with pcpu_reclaim_populated(), we are now calling pcpu_depopulate_chunk() during the active lifecycle of a chunk. Therefore, we need to flush the tlb as well otherwise we can end up accessing the wrong page through an invalid tlb mapping as reported in [1]. [1] https://lore.kernel.org/lkml/20210702191140.GA3166599@roeck-us.net/ Fixes: f183324133ea ("percpu: implement partial chunk depopulation") Reported-and-tested-by: Guenter Roeck Signed-off-by: Dennis Zhou --- mm/percpu-km.c | 6 ++++++ mm/percpu-vm.c | 5 +++-- mm/percpu.c | 32 ++++++++++++++++++++++++++------ 3 files changed, 35 insertions(+), 8 deletions(-) diff --git a/mm/percpu-km.c b/mm/percpu-km.c index c9d529dc7651f..fe31aa19db81a 100644 --- a/mm/percpu-km.c +++ b/mm/percpu-km.c @@ -32,6 +32,12 @@ #include +static void pcpu_post_unmap_tlb_flush(struct pcpu_chunk *chunk, + int page_start, int page_end) +{ + /* nothing */ +} + static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int page_start, int page_end, gfp_t gfp) { diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c index ee5d89fcd66f2..2054c9213c433 100644 --- a/mm/percpu-vm.c +++ b/mm/percpu-vm.c @@ -303,6 +303,9 @@ static int pcpu_populate_chunk(struct pcpu_chunk *chunk, * For each cpu, depopulate and unmap pages [@page_start,@page_end) * from @chunk. * + * Caller is required to call pcpu_post_unmap_tlb_flush() if not returning the + * region back to vmalloc() which will lazily flush the tlb. + * * CONTEXT: * pcpu_alloc_mutex. */ @@ -324,8 +327,6 @@ static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk, pcpu_unmap_pages(chunk, pages, page_start, page_end); - /* no need to flush tlb, vmalloc will handle it lazily */ - pcpu_free_pages(chunk, pages, page_start, page_end); } diff --git a/mm/percpu.c b/mm/percpu.c index b4cebeca4c0c1..7f2e0151c4e25 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -1572,6 +1572,7 @@ static void pcpu_chunk_depopulated(struct pcpu_chunk *chunk, * * pcpu_populate_chunk - populate the specified range of a chunk * pcpu_depopulate_chunk - depopulate the specified range of a chunk + * pcpu_post_unmap_tlb_flush - flush tlb for the specified range of a chunk * pcpu_create_chunk - create a new chunk * pcpu_destroy_chunk - destroy a chunk, always preceded by full depop * pcpu_addr_to_page - translate address to physical address @@ -1581,6 +1582,8 @@ static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int page_start, int page_end, gfp_t gfp); static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk, int page_start, int page_end); +static void pcpu_post_unmap_tlb_flush(struct pcpu_chunk *chunk, + int page_start, int page_end); static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp); static void pcpu_destroy_chunk(struct pcpu_chunk *chunk); static struct page *pcpu_addr_to_page(void *addr); @@ -2137,11 +2140,12 @@ static void pcpu_reclaim_populated(void) { struct pcpu_chunk *chunk; struct pcpu_block_md *block; + int freed_page_start, freed_page_end; int i, end; + bool reintegrate; lockdep_assert_held(&pcpu_lock); -restart: /* * Once a chunk is isolated to the to_depopulate list, the chunk is no * longer discoverable to allocations whom may populate pages. The only @@ -2157,6 +2161,9 @@ restart: * Scan chunk's pages in the reverse order to keep populated * pages close to the beginning of the chunk. */ + freed_page_start = chunk->nr_pages; + freed_page_end = 0; + reintegrate = false; for (i = chunk->nr_pages - 1, end = -1; i >= 0; i--) { /* no more work to do */ if (chunk->nr_empty_pop_pages == 0) @@ -2164,8 +2171,8 @@ restart: /* reintegrate chunk to prevent atomic alloc failures */ if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_HIGH) { - pcpu_reintegrate_chunk(chunk); - goto restart; + reintegrate = true; + goto end_chunk; } /* @@ -2194,16 +2201,29 @@ restart: spin_lock_irq(&pcpu_lock); pcpu_chunk_depopulated(chunk, i + 1, end + 1); + freed_page_start = min(freed_page_start, i + 1); + freed_page_end = max(freed_page_end, end + 1); /* reset the range and continue */ end = -1; } - if (chunk->free_bytes == pcpu_unit_size) +end_chunk: + /* batch tlb flush per chunk to amortize cost */ + if (freed_page_start < freed_page_end) { + spin_unlock_irq(&pcpu_lock); + pcpu_post_unmap_tlb_flush(chunk, + freed_page_start, + freed_page_end); + cond_resched(); + spin_lock_irq(&pcpu_lock); + } + + if (reintegrate || chunk->free_bytes == pcpu_unit_size) pcpu_reintegrate_chunk(chunk); else - list_move(&chunk->list, - &pcpu_chunk_lists[pcpu_sidelined_slot]); + list_move_tail(&chunk->list, + &pcpu_chunk_lists[pcpu_sidelined_slot]); } } -- 2.39.5