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From: Peter Xu <peterx@redhat.com>
To: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: David Hildenbrand <david@redhat.com>,
	Hugh Dickins <hughd@google.com>, Maya Gokhale <gokhale2@llnl.gov>,
	Jerome Glisse <jglisse@redhat.com>,
	Pavel Emelyanov <xemul@virtuozzo.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	peterx@redhat.com, Martin Cracauer <cracauer@cons.org>,
	Shaohua Li <shli@fb.com>, Andrea Arcangeli <aarcange@redhat.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Denis Plotnikov <dplotnikov@virtuozzo.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	Marty McFadden <mcfadden8@llnl.gov>, Mel Gorman <mgorman@suse.de>,
	"Kirill A . Shutemov" <kirill@shutemov.name>,
	"Dr . David Alan Gilbert" <dgilbert@redhat.com>
Subject: [PATCH v3 18/28] khugepaged: skip collapse if uffd-wp detected
Date: Wed, 20 Mar 2019 10:06:32 +0800	[thread overview]
Message-ID: <20190320020642.4000-19-peterx@redhat.com> (raw)
In-Reply-To: <20190320020642.4000-1-peterx@redhat.com>

Don't collapse the huge PMD if there is any userfault write protected
small PTEs.  The problem is that the write protection is in small page
granularity and there's no way to keep all these write protection
information if the small pages are going to be merged into a huge PMD.

The same thing needs to be considered for swap entries and migration
entries.  So do the check as well disregarding khugepaged_max_ptes_swap.

Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 include/trace/events/huge_memory.h |  1 +
 mm/khugepaged.c                    | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
index dd4db334bd63..2d7bad9cb976 100644
--- a/include/trace/events/huge_memory.h
+++ b/include/trace/events/huge_memory.h
@@ -13,6 +13,7 @@
 	EM( SCAN_PMD_NULL,		"pmd_null")			\
 	EM( SCAN_EXCEED_NONE_PTE,	"exceed_none_pte")		\
 	EM( SCAN_PTE_NON_PRESENT,	"pte_non_present")		\
+	EM( SCAN_PTE_UFFD_WP,		"pte_uffd_wp")			\
 	EM( SCAN_PAGE_RO,		"no_writable_page")		\
 	EM( SCAN_LACK_REFERENCED_PAGE,	"lack_referenced_page")		\
 	EM( SCAN_PAGE_NULL,		"page_null")			\
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 4f017339ddb2..396c7e4da83e 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -29,6 +29,7 @@ enum scan_result {
 	SCAN_PMD_NULL,
 	SCAN_EXCEED_NONE_PTE,
 	SCAN_PTE_NON_PRESENT,
+	SCAN_PTE_UFFD_WP,
 	SCAN_PAGE_RO,
 	SCAN_LACK_REFERENCED_PAGE,
 	SCAN_PAGE_NULL,
@@ -1123,6 +1124,15 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
 		pte_t pteval = *_pte;
 		if (is_swap_pte(pteval)) {
 			if (++unmapped <= khugepaged_max_ptes_swap) {
+				/*
+				 * Always be strict with uffd-wp
+				 * enabled swap entries.  Please see
+				 * comment below for pte_uffd_wp().
+				 */
+				if (pte_swp_uffd_wp(pteval)) {
+					result = SCAN_PTE_UFFD_WP;
+					goto out_unmap;
+				}
 				continue;
 			} else {
 				result = SCAN_EXCEED_SWAP_PTE;
@@ -1142,6 +1152,19 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
 			result = SCAN_PTE_NON_PRESENT;
 			goto out_unmap;
 		}
+		if (pte_uffd_wp(pteval)) {
+			/*
+			 * Don't collapse the page if any of the small
+			 * PTEs are armed with uffd write protection.
+			 * Here we can also mark the new huge pmd as
+			 * write protected if any of the small ones is
+			 * marked but that could bring uknown
+			 * userfault messages that falls outside of
+			 * the registered range.  So, just be simple.
+			 */
+			result = SCAN_PTE_UFFD_WP;
+			goto out_unmap;
+		}
 		if (pte_write(pteval))
 			writable = true;
 
-- 
2.17.1


  parent reply	other threads:[~2019-03-20  2:09 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-20  2:06 [PATCH v3 00/28] userfaultfd: write protection support Peter Xu
2019-03-20  2:06 ` [PATCH v3 01/28] mm: gup: rename "nonblocking" to "locked" where proper Peter Xu
2019-03-20  2:06 ` [PATCH v3 02/28] mm: userfault: return VM_FAULT_RETRY on signals Peter Xu
2019-03-20  2:06 ` [PATCH v3 03/28] userfaultfd: don't retake mmap_sem to emulate NOPAGE Peter Xu
2019-03-20  2:06 ` [PATCH v3 04/28] mm: allow VM_FAULT_RETRY for multiple times Peter Xu
2019-04-18 20:11   ` Jerome Glisse
2019-04-19  6:00     ` Peter Xu
2019-03-20  2:06 ` [PATCH v3 05/28] mm: gup: " Peter Xu
2019-03-20  2:06 ` [PATCH v3 06/28] userfaultfd: wp: add helper for writeprotect check Peter Xu
2019-03-20  2:06 ` [PATCH v3 07/28] userfaultfd: wp: hook userfault handler to write protection fault Peter Xu
2019-04-18 20:03   ` Jerome Glisse
2019-03-20  2:06 ` [PATCH v3 08/28] userfaultfd: wp: add WP pagetable tracking to x86 Peter Xu
2019-03-20  2:06 ` [PATCH v3 09/28] userfaultfd: wp: userfaultfd_pte/huge_pmd_wp() helpers Peter Xu
2019-03-20  2:06 ` [PATCH v3 10/28] userfaultfd: wp: add UFFDIO_COPY_MODE_WP Peter Xu
2019-03-20  2:06 ` [PATCH v3 11/28] mm: merge parameters for change_protection() Peter Xu
2019-03-20  2:06 ` [PATCH v3 12/28] userfaultfd: wp: apply _PAGE_UFFD_WP bit Peter Xu
2019-03-20  2:06 ` [PATCH v3 13/28] mm: export wp_page_copy() Peter Xu
2019-03-20  2:06 ` [PATCH v3 14/28] userfaultfd: wp: handle COW properly for uffd-wp Peter Xu
2019-04-18 20:51   ` Jerome Glisse
2019-04-19  6:26     ` Peter Xu
2019-04-19 15:02       ` Jerome Glisse
2019-04-22 12:20         ` Peter Xu
2019-04-22 14:54           ` Jerome Glisse
2019-04-23  3:00             ` Peter Xu
2019-04-23 15:34               ` Jerome Glisse
2019-04-24  8:38                 ` Peter Xu
2019-03-20  2:06 ` [PATCH v3 15/28] userfaultfd: wp: drop _PAGE_UFFD_WP properly when fork Peter Xu
2019-03-20  2:06 ` [PATCH v3 16/28] userfaultfd: wp: add pmd_swp_*uffd_wp() helpers Peter Xu
2019-03-20  2:06 ` [PATCH v3 17/28] userfaultfd: wp: support swap and page migration Peter Xu
2019-04-18 20:59   ` Jerome Glisse
2019-04-19  7:42     ` Peter Xu
2019-04-19 15:08       ` Jerome Glisse
2019-04-22 12:23         ` Peter Xu
2019-03-20  2:06 ` Peter Xu [this message]
2019-03-20  2:06 ` [PATCH v3 19/28] userfaultfd: introduce helper vma_find_uffd Peter Xu
2019-03-20  2:06 ` [PATCH v3 20/28] userfaultfd: wp: support write protection for userfault vma range Peter Xu
2019-03-20  2:06 ` [PATCH v3 21/28] userfaultfd: wp: add the writeprotect API to userfaultfd ioctl Peter Xu
2019-03-20  2:06 ` [PATCH v3 22/28] userfaultfd: wp: enabled write protection in userfaultfd API Peter Xu
2019-03-22 21:37   ` Mike Rapoport
2019-03-20  2:06 ` [PATCH v3 23/28] userfaultfd: wp: don't wake up when doing write protect Peter Xu
2019-03-20  2:06 ` [PATCH v3 24/28] userfaultfd: wp: UFFDIO_REGISTER_MODE_WP documentation update Peter Xu
2019-03-22 21:46   ` Mike Rapoport
2019-03-20  2:06 ` [PATCH v3 25/28] userfaultfd: wp: fixup swap entries in change_pte_range Peter Xu
2019-04-18 21:01   ` Jerome Glisse
2019-03-20  2:06 ` [PATCH v3 26/28] userfaultfd: wp: declare _UFFDIO_WRITEPROTECT conditionally Peter Xu
2019-03-22 21:43   ` Mike Rapoport
2019-03-20  2:06 ` [PATCH v3 27/28] userfaultfd: selftests: refactor statistics Peter Xu
2019-03-20  2:06 ` [PATCH v3 28/28] userfaultfd: selftests: add write-protect test Peter Xu
2019-04-09  6:08 ` [PATCH v3 00/28] userfaultfd: write protection support Peter Xu
2019-04-18 21:07   ` Jerome Glisse
2019-04-19  7:53     ` Peter Xu

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