[RFC 13/20] mm/tlb: introduce tlb_start_ptes() and tlb_end_ptes()

From: Nadav Amit <nadav.amit@gmail.com>
To: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: Nadav Amit <namit@vmware.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Will Deacon <will@kernel.org>, Yu Zhao <yuzhao@google.com>,
	Nick Piggin <npiggin@gmail.com>,
	x86@kernel.org
Subject: [RFC 13/20] mm/tlb: introduce tlb_start_ptes() and tlb_end_ptes()
Date: Sat, 30 Jan 2021 16:11:25 -0800	[thread overview]
Message-ID: <20210131001132.3368247-14-namit@vmware.com> (raw)
In-Reply-To: <20210131001132.3368247-1-namit@vmware.com>

From: Nadav Amit <namit@vmware.com>

Introduce tlb_start_ptes() and tlb_end_ptes() which would be called
before and after PTEs are updated and TLB flushes are deferred. This
will be later be used for fine granualrity deferred TLB flushing
detection.

In the meanwhile, move flush_tlb_batched_pending() into
tlb_start_ptes(). It was not called from mapping_dirty_helpers by
wp_pte() and clean_record_pte(), which might be a bug.

No additional functional change is intended.

Signed-off-by: Nadav Amit <namit@vmware.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Nick Piggin <npiggin@gmail.com>
Cc: x86@kernel.org
---
 fs/proc/task_mmu.c         |  2 ++
 include/asm-generic/tlb.h  | 18 ++++++++++++++++++
 mm/madvise.c               |  6 ++++--
 mm/mapping_dirty_helpers.c | 15 +++++++++++++--
 mm/memory.c                |  2 ++
 mm/mprotect.c              |  3 ++-
 6 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 4cd048ffa0f6..d0cce961fa5c 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1168,6 +1168,7 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
 		return 0;
 
 	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+	tlb_start_ptes(&cp->tlb);
 	for (; addr != end; pte++, addr += PAGE_SIZE) {
 		ptent = *pte;
 
@@ -1190,6 +1191,7 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
 		tlb_flush_pte_range(&cp->tlb, addr, PAGE_SIZE);
 		ClearPageReferenced(page);
 	}
+	tlb_end_ptes(&cp->tlb);
 	pte_unmap_unlock(pte - 1, ptl);
 	cond_resched();
 	return 0;
diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index 041be2ef4426..10690763090a 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -58,6 +58,11 @@
  *    Defaults to flushing at tlb_end_vma() to reset the range; helps when
  *    there's large holes between the VMAs.
  *
+ *  - tlb_start_ptes() / tlb_end_ptes; makr the start / end of PTEs change.
+ *
+ *    Does internal accounting to allow fine(r) granularity checks for
+ *    pte_accessible() on certain configuration.
+ *
  *  - tlb_remove_table()
  *
  *    tlb_remove_table() is the basic primitive to free page-table directories
@@ -373,6 +378,10 @@ static inline void tlb_flush(struct mmu_gather *tlb)
 		flush_tlb_range(tlb->vma, tlb->start, tlb->end);
 	}
 }
+#endif
+
+#if __is_defined(tlb_flush) ||						\
+	IS_ENABLED(CONFIG_ARCH_WANT_AGGRESSIVE_TLB_FLUSH_BATCHING)
 
 static inline void
 tlb_update_vma(struct mmu_gather *tlb, struct vm_area_struct *vma)
@@ -523,6 +532,15 @@ static inline void mark_mm_tlb_gen_done(struct mm_struct *mm, u64 gen)
 
 #endif /* CONFIG_ARCH_HAS_TLB_GENERATIONS */
 
+#define tlb_start_ptes(tlb)						\
+	do {								\
+		struct mmu_gather *_tlb = (tlb);			\
+									\
+		flush_tlb_batched_pending(_tlb->mm);			\
+	} while (0)
+
+static inline void tlb_end_ptes(struct mmu_gather *tlb) { }
+
 /*
  * tlb_flush_{pte|pmd|pud|p4d}_range() adjust the tlb->start and tlb->end,
  * and set corresponding cleared_*.
diff --git a/mm/madvise.c b/mm/madvise.c
index 0938fd3ad228..932c1c2eb9a3 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -392,7 +392,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 #endif
 	tlb_change_page_size(tlb, PAGE_SIZE);
 	orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
-	flush_tlb_batched_pending(mm);
+	tlb_start_ptes(tlb);
 	arch_enter_lazy_mmu_mode();
 	for (; addr < end; pte++, addr += PAGE_SIZE) {
 		ptent = *pte;
@@ -468,6 +468,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 	}
 
 	arch_leave_lazy_mmu_mode();
+	tlb_end_ptes(tlb);
 	pte_unmap_unlock(orig_pte, ptl);
 	if (pageout)
 		reclaim_pages(&page_list);
@@ -588,7 +589,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 
 	tlb_change_page_size(tlb, PAGE_SIZE);
 	orig_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
-	flush_tlb_batched_pending(mm);
+	tlb_start_ptes(tlb);
 	arch_enter_lazy_mmu_mode();
 	for (; addr != end; pte++, addr += PAGE_SIZE) {
 		ptent = *pte;
@@ -692,6 +693,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 		add_mm_counter(mm, MM_SWAPENTS, nr_swap);
 	}
 	arch_leave_lazy_mmu_mode();
+	tlb_end_ptes(tlb);
 	pte_unmap_unlock(orig_pte, ptl);
 	cond_resched();
 next:
diff --git a/mm/mapping_dirty_helpers.c b/mm/mapping_dirty_helpers.c
index 2ce6cf431026..063419ade304 100644
--- a/mm/mapping_dirty_helpers.c
+++ b/mm/mapping_dirty_helpers.c
@@ -6,6 +6,8 @@
 #include <asm/cacheflush.h>
 #include <asm/tlb.h>
 
+#include "internal.h"
+
 /**
  * struct wp_walk - Private struct for pagetable walk callbacks
  * @range: Range for mmu notifiers
@@ -36,7 +38,10 @@ static int wp_pte(pte_t *pte, unsigned long addr, unsigned long end,
 	pte_t ptent = *pte;
 
 	if (pte_write(ptent)) {
-		pte_t old_pte = ptep_modify_prot_start(walk->vma, addr, pte);
+		pte_t old_pte;
+
+		tlb_start_ptes(&wpwalk->tlb);
+		old_pte = ptep_modify_prot_start(walk->vma, addr, pte);
 
 		ptent = pte_wrprotect(old_pte);
 		ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent);
@@ -44,6 +49,7 @@ static int wp_pte(pte_t *pte, unsigned long addr, unsigned long end,
 
 		if (pte_may_need_flush(old_pte, ptent))
 			tlb_flush_pte_range(&wpwalk->tlb, addr, PAGE_SIZE);
+		tlb_end_ptes(&wpwalk->tlb);
 	}
 
 	return 0;
@@ -94,13 +100,18 @@ static int clean_record_pte(pte_t *pte, unsigned long addr,
 	if (pte_dirty(ptent)) {
 		pgoff_t pgoff = ((addr - walk->vma->vm_start) >> PAGE_SHIFT) +
 			walk->vma->vm_pgoff - cwalk->bitmap_pgoff;
-		pte_t old_pte = ptep_modify_prot_start(walk->vma, addr, pte);
+		pte_t old_pte;
+
+		tlb_start_ptes(&wpwalk->tlb);
+
+		old_pte = ptep_modify_prot_start(walk->vma, addr, pte);
 
 		ptent = pte_mkclean(old_pte);
 		ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent);
 
 		wpwalk->total++;
 		tlb_flush_pte_range(&wpwalk->tlb, addr, PAGE_SIZE);
+		tlb_end_ptes(&wpwalk->tlb);
 
 		__set_bit(pgoff, cwalk->bitmap);
 		cwalk->start = min(cwalk->start, pgoff);
diff --git a/mm/memory.c b/mm/memory.c
index 9e8576a83147..929a93c50d9a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1221,6 +1221,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 	init_rss_vec(rss);
 	start_pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
 	pte = start_pte;
+	tlb_start_ptes(tlb);
 	flush_tlb_batched_pending(mm);
 	arch_enter_lazy_mmu_mode();
 	do {
@@ -1314,6 +1315,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 	add_mm_rss_vec(mm, rss);
 	arch_leave_lazy_mmu_mode();
 
+	tlb_end_ptes(tlb);
 	/* Do the actual TLB flush before dropping ptl */
 	if (force_flush)
 		tlb_flush_mmu_tlbonly(tlb);
diff --git a/mm/mprotect.c b/mm/mprotect.c
index b7473d2c9a1f..1258bbe42ee1 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -70,7 +70,7 @@ static unsigned long change_pte_range(struct mmu_gather *tlb,
 	    atomic_read(&vma->vm_mm->mm_users) == 1)
 		target_node = numa_node_id();
 
-	flush_tlb_batched_pending(vma->vm_mm);
+	tlb_start_ptes(tlb);
 	arch_enter_lazy_mmu_mode();
 	do {
 		oldpte = *pte;
@@ -182,6 +182,7 @@ static unsigned long change_pte_range(struct mmu_gather *tlb,
 		}
 	} while (pte++, addr += PAGE_SIZE, addr != end);
 	arch_leave_lazy_mmu_mode();
+	tlb_end_ptes(tlb);
 	pte_unmap_unlock(pte - 1, ptl);
 
 	return pages;
-- 
2.25.1

