linux-kernel - [PATCH 4.14 009/210] mm/migrate_device.c: flush TLB while holding PTL

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Message-Id: <20221024112957.183720272@linuxfoundation.org>
Date:   Mon, 24 Oct 2022 13:28:46 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Alistair Popple <apopple@...dia.com>,
        Nadav Amit <nadav.amit@...il.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Alex Sierra <alex.sierra@....com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        huang ying <huang.ying.caritas@...il.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Karol Herbst <kherbst@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Lyude Paul <lyude@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Paul Mackerras <paulus@...abs.org>,
        Ralph Campbell <rcampbell@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 4.14 009/210] mm/migrate_device.c: flush TLB while holding PTL

From: Alistair Popple <apopple@...dia.com>

commit 60bae73708963de4a17231077285bd9ff2f41c44 upstream.

When clearing a PTE the TLB should be flushed whilst still holding the PTL
to avoid a potential race with madvise/munmap/etc.  For example consider
the following sequence:

  CPU0                          CPU1
  ----                          ----

  migrate_vma_collect_pmd()
  pte_unmap_unlock()
                                madvise(MADV_DONTNEED)
                                -> zap_pte_range()
                                pte_offset_map_lock()
                                [ PTE not present, TLB not flushed ]
                                pte_unmap_unlock()
                                [ page is still accessible via stale TLB ]
  flush_tlb_range()

In this case the page may still be accessed via the stale TLB entry after
madvise returns.  Fix this by flushing the TLB while holding the PTL.

Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages")
Link: https://lkml.kernel.org/r/9f801e9d8d830408f2ca27821f606e09aa856899.1662078528.git-series.apopple@nvidia.com
Signed-off-by: Alistair Popple <apopple@...dia.com>
Reported-by: Nadav Amit <nadav.amit@...il.com>
Reviewed-by: "Huang, Ying" <ying.huang@...el.com>
Acked-by: David Hildenbrand <david@...hat.com>
Acked-by: Peter Xu <peterx@...hat.com>
Cc: Alex Sierra <alex.sierra@....com>
Cc: Ben Skeggs <bskeggs@...hat.com>
Cc: Felix Kuehling <Felix.Kuehling@....com>
Cc: huang ying <huang.ying.caritas@...il.com>
Cc: Jason Gunthorpe <jgg@...dia.com>
Cc: John Hubbard <jhubbard@...dia.com>
Cc: Karol Herbst <kherbst@...hat.com>
Cc: Logan Gunthorpe <logang@...tatee.com>
Cc: Lyude Paul <lyude@...hat.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Paul Mackerras <paulus@...abs.org>
Cc: Ralph Campbell <rcampbell@...dia.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/migrate.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2349,13 +2349,14 @@ next:
 		migrate->dst[migrate->npages] = 0;
 		migrate->src[migrate->npages++] = mpfn;
 	}
-	arch_leave_lazy_mmu_mode();
-	pte_unmap_unlock(ptep - 1, ptl);
 
 	/* Only flush the TLB if we actually modified any entries */
 	if (unmapped)
 		flush_tlb_range(walk->vma, start, end);
 
+	arch_leave_lazy_mmu_mode();
+	pte_unmap_unlock(ptep - 1, ptl);
+
 	return 0;
 }