From 912efa17e5121693dfbadae29768f4144a3f9e62 Mon Sep 17 00:00:00 2001
From: Will Deacon <will@kernel.org>
Date: Wed, 27 Jan 2021 23:53:42 +0000
Subject: [PATCH] mm: proc: Invalidate TLB after clearing soft-dirty page state

References: bsc#1163776 ltc#183929 git-fixes
Patch-mainline: v5.12-rc1
Git-commit: 912efa17e5121693dfbadae29768f4144a3f9e62

Since commit 0758cd830494 ("asm-generic/tlb: avoid potential double
flush"), TLB invalidation is elided in tlb_finish_mmu() if no entries
were batched via the tlb_remove_*() functions. Consequently, the
page-table modifications performed by clear_refs_write() in response to
a write to /proc/<pid>/clear_refs do not perform TLB invalidation.
Although this is fine when simply aging the ptes, in the case of
clearing the "soft-dirty" state we can end up with entries where
pte_write() is false, yet a writable mapping remains in the TLB.

Fix this by avoiding the mmu_gather API altogether: managing both the
'tlb_flush_pending' flag on the 'mm_struct' and explicit TLB
invalidation for the sort-dirty path, much like mprotect() does already.

Fixes: 0758cd830494 ("asm-generic/tlb: avoid potential double flush”)
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Yu Zhao <yuzhao@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lkml.kernel.org/r/20210127235347.1402-2-will@kernel.org
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 fs/proc/task_mmu.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1126,7 +1126,6 @@ static ssize_t clear_refs_write(struct f
 	struct mm_struct *mm;
 	struct vm_area_struct *vma;
 	enum clear_refs_types type;
-	struct mmu_gather tlb;
 	int itype;
 	int rv;
 
@@ -1177,7 +1176,6 @@ static ssize_t clear_refs_write(struct f
 			count = -EINTR;
 			goto out_mm;
 		}
-		tlb_gather_mmu(&tlb, mm, 0, -1);
 		if (type == CLEAR_REFS_SOFT_DIRTY) {
 			for (vma = mm->mmap; vma; vma = vma->vm_next) {
 				if (!(vma->vm_flags & VM_SOFTDIRTY))
@@ -1213,15 +1211,18 @@ static ssize_t clear_refs_write(struct f
 				break;
 			}
 
+			inc_tlb_flush_pending(mm);
 			mmu_notifier_range_init(&range, MMU_NOTIFY_SOFT_DIRTY,
 						0, NULL, mm, 0, -1UL);
 			mmu_notifier_invalidate_range_start(&range);
 		}
 		walk_page_range(mm, 0, mm->highest_vm_end, &clear_refs_walk_ops,
 				&cp);
-		if (type == CLEAR_REFS_SOFT_DIRTY)
+		if (type == CLEAR_REFS_SOFT_DIRTY) {
 			mmu_notifier_invalidate_range_end(&range);
-		tlb_finish_mmu(&tlb, 0, -1);
+			flush_tlb_mm(mm);
+			dec_tlb_flush_pending(mm);
+		}
 		up_read(&mm->mmap_sem);
 out_mm:
 		mmput(mm);