From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Mike Rapoport <rppt@kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Matthew Wilcox <willy@infradead.org>,
David Hildenbrand <david@redhat.com>,
Suren Baghdasaryan <surenb@google.com>,
Qi Zheng <zhengqi.arch@bytedance.com>,
Yang Shi <shy828301@gmail.com>,
Mel Gorman <mgorman@techsingularity.net>,
Peter Xu <peterx@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will@kernel.org>, Yu Zhao <yuzhao@google.com>,
Alistair Popple <apopple@nvidia.com>,
Ralph Campbell <rcampbell@nvidia.com>,
Ira Weiny <ira.weiny@intel.com>,
Steven Price <steven.price@arm.com>,
SeongJae Park <sj@kernel.org>,
Lorenzo Stoakes <lstoakes@gmail.com>,
Huang Ying <ying.huang@intel.com>,
Naoya Horiguchi <naoya.horiguchi@nec.com>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Zack Rusin <zackr@vmware.com>, Jason Gunthorpe <jgg@ziepe.ca>,
Axel Rasmussen <axelrasmussen@google.com>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Pasha Tatashin <pasha.tatashin@soleen.com>,
Miaohe Lin <linmiaohe@huawei.com>,
Minchan Kim <minchan@kernel.org>,
Christoph Hellwig <hch@infradead.org>, Song Liu <song@kernel.org>,
Thomas Hellstrom <thomas.hellstrom@linux.intel.com>,
Russell King <linux@armlinux.org.uk>,
"David Sc. Miller" <davem@davemloft.net>,
Michael Ellerman <mpe@ellerman.id.au>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
Heiko Carstens <hca@linux.ibm.com>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Claudio Imbrenda <imbrenda@linux.ibm.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Jann Horn <jannh@google.com>,
Vishal Moola <vishal.moola@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
linux-arm-kernel@lists.infradead.org, sparclinux@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH v2 02/12] mm/pgtable: add PAE safety to __pte_offset_map()
Date: Tue, 20 Jun 2023 00:42:13 -0700 (PDT) [thread overview]
Message-ID: <df1884ce-93c-efa-2354-4d749eb25f1@google.com> (raw)
In-Reply-To: <54cb04f-3762-987f-8294-91dafd8ebfb0@google.com>
There is a faint risk that __pte_offset_map(), on a 32-bit architecture
with a 64-bit pmd_t e.g. x86-32 with CONFIG_X86_PAE=y, would succeed on
a pmdval assembled from a pmd_low and a pmd_high which never belonged
together: their combination not pointing to a page table at all, perhaps
not even a valid pfn. pmdp_get_lockless() is not enough to prevent that.
Guard against that (on such configs) by local_irq_save() blocking TLB
flush between present updates, as linux/pgtable.h suggests. It's only
needed around the pmdp_get_lockless() in __pte_offset_map(): a race when
__pte_offset_map_lock() repeats the pmdp_get_lockless() after getting the
lock, would just send it back to __pte_offset_map() again.
Complement this pmdp_get_lockless_start() and pmdp_get_lockless_end(),
used only locally in __pte_offset_map(), with a pmdp_get_lockless_sync()
synonym for tlb_remove_table_sync_one(): to send the necessary interrupt
at the right moment on those configs which do not already send it.
CONFIG_GUP_GET_PXX_LOW_HIGH is enabled when required by mips, sh and x86.
It is not enabled by arm-32 CONFIG_ARM_LPAE: my understanding is that
Will Deacon's 2020 enhancements to READ_ONCE() are sufficient for arm.
It is not enabled by arc, but its pmd_t is 32-bit even when pte_t 64-bit.
Limit the IRQ disablement to CONFIG_HIGHPTE? Perhaps, but would need a
little more work, to retry if pmd_low good for page table, but pmd_high
non-zero from THP (and that might be making x86-specific assumptions).
Signed-off-by: Hugh Dickins <hughd@google.com>
---
include/linux/pgtable.h | 4 ++++
mm/pgtable-generic.c | 29 +++++++++++++++++++++++++++++
2 files changed, 33 insertions(+)
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 8b0fc7fdc46f..525f1782b466 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -390,6 +390,7 @@ static inline pmd_t pmdp_get_lockless(pmd_t *pmdp)
return pmd;
}
#define pmdp_get_lockless pmdp_get_lockless
+#define pmdp_get_lockless_sync() tlb_remove_table_sync_one()
#endif /* CONFIG_PGTABLE_LEVELS > 2 */
#endif /* CONFIG_GUP_GET_PXX_LOW_HIGH */
@@ -408,6 +409,9 @@ static inline pmd_t pmdp_get_lockless(pmd_t *pmdp)
{
return pmdp_get(pmdp);
}
+static inline void pmdp_get_lockless_sync(void)
+{
+}
#endif
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
index 674671835631..5e85a625ab30 100644
--- a/mm/pgtable-generic.c
+++ b/mm/pgtable-generic.c
@@ -232,12 +232,41 @@ pmd_t pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long address,
#endif
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+#if defined(CONFIG_GUP_GET_PXX_LOW_HIGH) && \
+ (defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RCU))
+/*
+ * See the comment above ptep_get_lockless() in include/linux/pgtable.h:
+ * the barriers in pmdp_get_lockless() cannot guarantee that the value in
+ * pmd_high actually belongs with the value in pmd_low; but holding interrupts
+ * off blocks the TLB flush between present updates, which guarantees that a
+ * successful __pte_offset_map() points to a page from matched halves.
+ */
+static unsigned long pmdp_get_lockless_start(void)
+{
+ unsigned long irqflags;
+
+ local_irq_save(irqflags);
+ return irqflags;
+}
+static void pmdp_get_lockless_end(unsigned long irqflags)
+{
+ local_irq_restore(irqflags);
+}
+#else
+static unsigned long pmdp_get_lockless_start(void) { return 0; }
+static void pmdp_get_lockless_end(unsigned long irqflags) { }
+#endif
+
pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp)
{
+ unsigned long irqflags;
pmd_t pmdval;
rcu_read_lock();
+ irqflags = pmdp_get_lockless_start();
pmdval = pmdp_get_lockless(pmd);
+ pmdp_get_lockless_end(irqflags);
+
if (pmdvalp)
*pmdvalp = pmdval;
if (unlikely(pmd_none(pmdval) || is_pmd_migration_entry(pmdval)))
--
2.35.3
next prev parent reply other threads:[~2023-06-20 7:43 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-20 7:35 [PATCH v2 00/12] mm: free retracted page table by RCU Hugh Dickins
2023-06-20 7:40 ` [PATCH v2 01/12] mm/pgtable: add rcu_read_lock() and rcu_read_unlock()s Hugh Dickins
2023-06-20 7:42 ` Hugh Dickins [this message]
2023-06-20 7:43 ` [PATCH v2 03/12] arm: adjust_pte() use pte_offset_map_nolock() Hugh Dickins
2023-06-20 7:45 ` [PATCH v2 04/12] powerpc: assert_pte_locked() " Hugh Dickins
2023-06-20 7:47 ` [PATCH v2 05/12] powerpc: add pte_free_defer() for pgtables sharing page Hugh Dickins
2023-06-20 11:45 ` Jason Gunthorpe
2023-06-20 19:54 ` Hugh Dickins
2023-06-20 23:52 ` Jason Gunthorpe
2023-06-22 2:36 ` Hugh Dickins
2023-06-27 17:01 ` Jason Gunthorpe
2023-06-27 20:53 ` Hugh Dickins
2023-06-20 7:49 ` [PATCH v2 06/12] sparc: add pte_free_defer() for pte_t *pgtable_t Hugh Dickins
2023-06-20 7:51 ` [PATCH v2 07/12] s390: add pte_free_defer() for pgtables sharing page Hugh Dickins
2023-06-28 19:16 ` Gerald Schaefer
2023-06-29 5:08 ` Hugh Dickins
2023-06-29 15:22 ` Jason Gunthorpe
2023-06-29 15:56 ` Gerald Schaefer
2023-06-30 6:00 ` Hugh Dickins
2023-07-02 4:32 ` Hugh Dickins
2023-07-04 13:40 ` Alexander Gordeev
2023-07-04 16:03 ` Hugh Dickins
2023-07-04 15:19 ` Gerald Schaefer
2023-07-04 17:03 ` Hugh Dickins
2023-07-05 12:55 ` Gerald Schaefer
2023-07-06 1:20 ` Hugh Dickins
2023-07-06 15:02 ` Gerald Schaefer
2023-07-06 19:45 ` Hugh Dickins
2023-07-10 17:21 ` Jason Gunthorpe
2023-07-05 6:46 ` Alexander Gordeev
2023-07-06 0:52 ` Hugh Dickins
2023-07-07 14:37 ` Gerald Schaefer
2023-07-03 16:10 ` Gerald Schaefer
2023-06-29 13:59 ` Alexander Gordeev
2023-06-29 15:43 ` Gerald Schaefer
2023-06-30 13:38 ` Claudio Imbrenda
2023-06-30 15:28 ` Hugh Dickins
2023-06-30 16:25 ` Claudio Imbrenda
2023-06-30 19:22 ` Hugh Dickins
2023-07-03 11:00 ` Claudio Imbrenda
2023-07-03 21:29 ` Jason Gunthorpe
2023-06-20 7:53 ` [PATCH v2 08/12] mm/pgtable: add pte_free_defer() for pgtable as page Hugh Dickins
2023-06-20 7:54 ` [PATCH v2 09/12] mm/khugepaged: retract_page_tables() without mmap or vma lock Hugh Dickins
2023-06-20 7:56 ` [PATCH v2 10/12] mm/khugepaged: collapse_pte_mapped_thp() with mmap_read_lock() Hugh Dickins
2023-06-20 8:04 ` [PATCH mm " Hugh Dickins
2023-06-20 7:58 ` [PATCH v2 11/12] mm/khugepaged: delete khugepaged_collapse_pte_mapped_thps() Hugh Dickins
2023-06-20 7:59 ` [PATCH v2 12/12] mm: delete mmap_write_trylock() and vma_try_start_write() Hugh Dickins
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