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authorPeter Xu <peterx@redhat.com>2022-05-12 20:22:53 -0700
committerAndrew Morton <akpm@linux-foundation.org>2022-05-13 07:20:10 -0700
commit999dad824c39ed14dee7c4412aae531ba9e74a90 (patch)
tree902b71da56121147d613e6ba249157ca5563e143 /mm/memory.c
parent9c28a205c06123b9f0a0c4d819ece9f5f552d004 (diff)
mm/shmem: persist uffd-wp bit across zapping for file-backed
File-backed memory is prone to being unmapped at any time. It means all information in the pte will be dropped, including the uffd-wp flag. To persist the uffd-wp flag, we'll use the pte markers. This patch teaches the zap code to understand uffd-wp and know when to keep or drop the uffd-wp bit. Add a new flag ZAP_FLAG_DROP_MARKER and set it in zap_details when we don't want to persist such an information, for example, when destroying the whole vma, or punching a hole in a shmem file. For the rest cases we should never drop the uffd-wp bit, or the wr-protect information will get lost. The new ZAP_FLAG_DROP_MARKER needs to be put into mm.h rather than memory.c because it'll be further referenced in hugetlb files later. Link: https://lkml.kernel.org/r/20220405014847.14295-1-peterx@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: "Kirill A . Shutemov" <kirill@shutemov.name> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Nadav Amit <nadav.amit@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/memory.c')
-rw-r--r--mm/memory.c49
1 files changed, 46 insertions, 3 deletions
diff --git a/mm/memory.c b/mm/memory.c
index c16f873373a2..ecb1d58dcaef 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -74,6 +74,7 @@
#include <linux/perf_event.h>
#include <linux/ptrace.h>
#include <linux/vmalloc.h>
+#include <linux/mm_inline.h>
#include <trace/events/kmem.h>
@@ -1306,6 +1307,7 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
struct zap_details {
struct folio *single_folio; /* Locked folio to be unmapped */
bool even_cows; /* Zap COWed private pages too? */
+ zap_flags_t zap_flags; /* Extra flags for zapping */
};
/* Whether we should zap all COWed (private) pages too */
@@ -1334,6 +1336,29 @@ static inline bool should_zap_page(struct zap_details *details, struct page *pag
return !PageAnon(page);
}
+static inline bool zap_drop_file_uffd_wp(struct zap_details *details)
+{
+ if (!details)
+ return false;
+
+ return details->zap_flags & ZAP_FLAG_DROP_MARKER;
+}
+
+/*
+ * This function makes sure that we'll replace the none pte with an uffd-wp
+ * swap special pte marker when necessary. Must be with the pgtable lock held.
+ */
+static inline void
+zap_install_uffd_wp_if_needed(struct vm_area_struct *vma,
+ unsigned long addr, pte_t *pte,
+ struct zap_details *details, pte_t pteval)
+{
+ if (zap_drop_file_uffd_wp(details))
+ return;
+
+ pte_install_uffd_wp_if_needed(vma, addr, pte, pteval);
+}
+
static unsigned long zap_pte_range(struct mmu_gather *tlb,
struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, unsigned long end,
@@ -1371,6 +1396,8 @@ again:
ptent = ptep_get_and_clear_full(mm, addr, pte,
tlb->fullmm);
tlb_remove_tlb_entry(tlb, pte, addr);
+ zap_install_uffd_wp_if_needed(vma, addr, pte, details,
+ ptent);
if (unlikely(!page))
continue;
@@ -1401,6 +1428,13 @@ again:
page = pfn_swap_entry_to_page(entry);
if (unlikely(!should_zap_page(details, page)))
continue;
+ /*
+ * Both device private/exclusive mappings should only
+ * work with anonymous page so far, so we don't need to
+ * consider uffd-wp bit when zap. For more information,
+ * see zap_install_uffd_wp_if_needed().
+ */
+ WARN_ON_ONCE(!vma_is_anonymous(vma));
rss[mm_counter(page)]--;
if (is_device_private_entry(entry))
page_remove_rmap(page, vma, false);
@@ -1417,8 +1451,10 @@ again:
if (!should_zap_page(details, page))
continue;
rss[mm_counter(page)]--;
- } else if (is_pte_marker_entry(entry)) {
- /* By default, simply drop all pte markers when zap */
+ } else if (pte_marker_entry_uffd_wp(entry)) {
+ /* Only drop the uffd-wp marker if explicitly requested */
+ if (!zap_drop_file_uffd_wp(details))
+ continue;
} else if (is_hwpoison_entry(entry)) {
if (!should_zap_cows(details))
continue;
@@ -1427,6 +1463,7 @@ again:
WARN_ON_ONCE(1);
}
pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
+ zap_install_uffd_wp_if_needed(vma, addr, pte, details, ptent);
} while (pte++, addr += PAGE_SIZE, addr != end);
add_mm_rss_vec(mm, rss);
@@ -1637,12 +1674,17 @@ void unmap_vmas(struct mmu_gather *tlb,
unsigned long end_addr)
{
struct mmu_notifier_range range;
+ struct zap_details details = {
+ .zap_flags = ZAP_FLAG_DROP_MARKER,
+ /* Careful - we need to zap private pages too! */
+ .even_cows = true,
+ };
mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm,
start_addr, end_addr);
mmu_notifier_invalidate_range_start(&range);
for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next)
- unmap_single_vma(tlb, vma, start_addr, end_addr, NULL);
+ unmap_single_vma(tlb, vma, start_addr, end_addr, &details);
mmu_notifier_invalidate_range_end(&range);
}
@@ -3438,6 +3480,7 @@ void unmap_mapping_folio(struct folio *folio)
details.even_cows = false;
details.single_folio = folio;
+ details.zap_flags = ZAP_FLAG_DROP_MARKER;
i_mmap_lock_read(mapping);
if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)))