+ mm-khugepaged-fix-gup-fast-interaction-by-sending-ipi.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/khugepaged: fix GUP-fast interaction by sending IPI
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-khugepaged-fix-gup-fast-interaction-by-sending-ipi.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-khugepaged-fix-gup-fast-interaction-by-sending-ipi.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Jann Horn <jannh@google.com>
Subject: mm/khugepaged: fix GUP-fast interaction by sending IPI
Date: Fri, 25 Nov 2022 22:37:13 +0100

Since commit 70cbc3cc78a99 ("mm: gup: fix the fast GUP race against THP
collapse"), the lockless_pages_from_mm() fastpath rechecks the pmd_t to
ensure that the page table was not removed by khugepaged in between.

However, lockless_pages_from_mm() still requires that the page table is
not concurrently freed.  Fix it by sending IPIs (if the architecture uses
semi-RCU-style page table freeing) before freeing/reusing page tables.

Link: https://lkml.kernel.org/r/20221125213714.4115729-2-jannh@google.com
Fixes: ba76149f47d8 ("thp: khugepaged")
Signed-off-by: Jann Horn <jannh@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/asm-generic/tlb.h |    4 ++++
 mm/khugepaged.c           |    2 ++
 mm/mmu_gather.c           |    4 +---
 3 files changed, 7 insertions(+), 3 deletions(-)

--- a/include/asm-generic/tlb.h~mm-khugepaged-fix-gup-fast-interaction-by-sending-ipi
+++ a/include/asm-generic/tlb.h
@@ -222,12 +222,16 @@ extern void tlb_remove_table(struct mmu_
 #define tlb_needs_table_invalidate() (true)
 #endif
 
+void tlb_remove_table_sync_one(void);
+
 #else
 
 #ifdef tlb_needs_table_invalidate
 #error tlb_needs_table_invalidate() requires MMU_GATHER_RCU_TABLE_FREE
 #endif
 
+static inline void tlb_remove_table_sync_one(void) { }
+
 #endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */
 
 
--- a/mm/khugepaged.c~mm-khugepaged-fix-gup-fast-interaction-by-sending-ipi
+++ a/mm/khugepaged.c
@@ -1051,6 +1051,7 @@ static int collapse_huge_page(struct mm_
 	_pmd = pmdp_collapse_flush(vma, address, pmd);
 	spin_unlock(pmd_ptl);
 	mmu_notifier_invalidate_range_end(&range);
+	tlb_remove_table_sync_one();
 
 	spin_lock(pte_ptl);
 	result =  __collapse_huge_page_isolate(vma, address, pte, cc,
@@ -1410,6 +1411,7 @@ static void collapse_and_free_pmd(struct
 		lockdep_assert_held_write(&vma->anon_vma->root->rwsem);
 
 	pmd = pmdp_collapse_flush(vma, addr, pmdp);
+	tlb_remove_table_sync_one();
 	mm_dec_nr_ptes(mm);
 	page_table_check_pte_clear_range(mm, addr, pmd);
 	pte_free(mm, pmd_pgtable(pmd));
--- a/mm/mmu_gather.c~mm-khugepaged-fix-gup-fast-interaction-by-sending-ipi
+++ a/mm/mmu_gather.c
@@ -153,7 +153,7 @@ static void tlb_remove_table_smp_sync(vo
 	/* Simply deliver the interrupt */
 }
 
-static void tlb_remove_table_sync_one(void)
+void tlb_remove_table_sync_one(void)
 {
 	/*
 	 * This isn't an RCU grace period and hence the page-tables cannot be
@@ -177,8 +177,6 @@ static void tlb_remove_table_free(struct
 
 #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);
_

Patches currently in -mm which might be from jannh@google.com are

mm-khugepaged-take-the-right-locks-for-page-table-retraction.patch
mm-khugepaged-fix-gup-fast-interaction-by-sending-ipi.patch
mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths.patch