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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id j200-20020a2523d1000000b00be6cf9d2544sm254636ybj.40.2023.06.20.00.42.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Jun 2023 00:42:18 -0700 (PDT) Date: Tue, 20 Jun 2023 00:42:13 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Andrew Morton cc: Gerald Schaefer , Vasily Gorbik , Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , Matthew Wilcox , David Hildenbrand , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Xu , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Lorenzo Stoakes , Huang Ying , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , Russell King , "David Sc. Miller" , Michael Ellerman , "Aneesh Kumar K.V" , Heiko Carstens , Christian Borntraeger , Claudio Imbrenda , Alexander Gordeev , Jann Horn , Vishal Moola , Vlastimil Babka , 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() In-Reply-To: <54cb04f-3762-987f-8294-91dafd8ebfb0@google.com> Message-ID: References: <54cb04f-3762-987f-8294-91dafd8ebfb0@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: C7F58160020 X-Stat-Signature: ci5x7hd83jgk68ok5spu66eokzmdqk6a X-Rspam-User: X-HE-Tag: 1687246939-379034 X-HE-Meta: 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 ++NvB1Xv 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 --- 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