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Thu, 03 Oct 2019 01:34:18 +0000 Received: from b03ledav004.gho.boulder.ibm.com (b03ledav004.gho.boulder.ibm.com [9.17.130.235]) by b03cxnp07029.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x931YGel37683522 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 3 Oct 2019 01:34:16 GMT Received: from b03ledav004.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 493EF7805C; Thu, 3 Oct 2019 01:34:16 +0000 (GMT) Received: from b03ledav004.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 663BE7805E; Thu, 3 Oct 2019 01:34:04 +0000 (GMT) Received: from LeoBras.ibmuc.com (unknown [9.85.174.224]) by b03ledav004.gho.boulder.ibm.com (Postfix) with ESMTP; Thu, 3 Oct 2019 01:34:04 +0000 (GMT) From: Leonardo Bras To: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v5 02/11] powerpc/mm: Adds counting method to monitor lockless pgtable walks Date: Wed, 2 Oct 2019 22:33:16 -0300 Message-Id: <20191003013325.2614-3-leonardo@linux.ibm.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20191003013325.2614-1-leonardo@linux.ibm.com> References: <20191003013325.2614-1-leonardo@linux.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-10-03_01:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1910030012 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Song Liu , Michal Hocko , "Peter Zijlstra \(Intel\)" , "Dmitry V. Levin" , Keith Busch , Paul Mackerras , Christoph Lameter , Ira Weiny , Thomas Gleixner , Elena Reshetova , Andrea Arcangeli , Santosh Sivaraj , Davidlohr Bueso , "Aneesh Kumar K.V" , Bartlomiej Zolnierkiewicz , Mike Rapoport , Jason Gunthorpe , Allison Randal , Mahesh Salgaonkar , Leonardo Bras , Alexey Dobriyan , Ingo Molnar , Ralph Campbell , Arnd Bergmann , Jann Horn , John Hubbard , Jesper Dangaard Brouer , Nicholas Piggin , =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= , Mathieu Desnoyers , Al Viro , Andrey Ryabinin , Dan Williams , Reza Arbab , Vlastimil Babka , Christian Brauner , Greg Kroah-Hartman , Souptick Joarder , Andrew Morton , Logan Gunthorpe , Roman Gushchin , "Kirill A. Shutemov" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" It's necessary to monitor lockless pagetable walks, in order to avoid doing THP splitting/collapsing during them. On powerpc, we need to do some lockless pagetable walks from functions that already have disabled interrupts, specially from real mode with MSR[EE=0]. In these contexts, disabling/enabling interrupts can be very troubling. So, this arch-specific implementation features functions with an extra argument that allows interrupt enable/disable to be skipped: __begin_lockless_pgtbl_walk() and __end_lockless_pgtbl_walk(). Functions similar to the generic ones are also exported, by calling the above functions with parameter *able_irq = false. While there is no config option, the method is disabled and these functions are only doing what was already needed to lockless pagetable walks (disabling interrupt). A memory barrier was also added just to make sure there is no speculative read outside the interrupt disabled area. Signed-off-by: Leonardo Bras --- arch/powerpc/include/asm/book3s/64/pgtable.h | 9 ++ arch/powerpc/mm/book3s64/pgtable.c | 117 +++++++++++++++++++ 2 files changed, 126 insertions(+) diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h index b01624e5c467..8330b35cd28d 100644 --- a/arch/powerpc/include/asm/book3s/64/pgtable.h +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h @@ -1372,5 +1372,14 @@ static inline bool pgd_is_leaf(pgd_t pgd) return !!(pgd_raw(pgd) & cpu_to_be64(_PAGE_PTE)); } +#define __HAVE_ARCH_LOCKLESS_PGTBL_WALK_CONTROL +unsigned long begin_lockless_pgtbl_walk(struct mm_struct *mm); +unsigned long __begin_lockless_pgtbl_walk(struct mm_struct *mm, + bool disable_irq); +void end_lockless_pgtbl_walk(struct mm_struct *mm, unsigned long irq_mask); +void __end_lockless_pgtbl_walk(struct mm_struct *mm, unsigned long irq_mask, + bool enable_irq); +int running_lockless_pgtbl_walk(struct mm_struct *mm); + #endif /* __ASSEMBLY__ */ #endif /* _ASM_POWERPC_BOOK3S_64_PGTABLE_H_ */ diff --git a/arch/powerpc/mm/book3s64/pgtable.c b/arch/powerpc/mm/book3s64/pgtable.c index 75483b40fcb1..ae557fdce9a3 100644 --- a/arch/powerpc/mm/book3s64/pgtable.c +++ b/arch/powerpc/mm/book3s64/pgtable.c @@ -98,6 +98,123 @@ void serialize_against_pte_lookup(struct mm_struct *mm) smp_call_function_many(mm_cpumask(mm), do_nothing, NULL, 1); } +/* + * Counting method to monitor lockless pagetable walks: + * Uses begin_lockless_pgtbl_walk and end_lockless_pgtbl_walk to track the + * number of lockless pgtable walks happening, and + * running_lockless_pgtbl_walk to return this value. + */ + +/* begin_lockless_pgtbl_walk: Must be inserted before a function call that does + * lockless pagetable walks, such as __find_linux_pte(). + * This version allows setting disable_irq=false, so irqs are not touched, which + * is quite useful for running when ints are already disabled (like real-mode) + */ + +inline unsigned long __begin_lockless_pgtbl_walk(struct mm_struct *mm, + bool disable_irq) +{ + unsigned long irq_mask = 0; + + if (IS_ENABLED(CONFIG_LOCKLESS_PAGE_TABLE_WALK_TRACKING)) + atomic_inc(&mm->lockless_pgtbl_walkers); + + /* + * Interrupts must be disabled during the lockless page table walk. + * That's because the deleting or splitting involves flushing TLBs, + * which in turn issues interrupts, that will block when disabled. + * + * When this function is called from realmode with MSR[EE=0], + * it's not needed to touch irq, since it's already disabled. + */ + if (disable_irq) + local_irq_save(irq_mask); + + /* + * This memory barrier pairs with any code that is either trying to + * delete page tables, or split huge pages. Without this barrier, + * the page tables could be read speculatively outside of interrupt + * disabling or reference counting. + */ + smp_mb(); + + return irq_mask; +} +EXPORT_SYMBOL(__begin_lockless_pgtbl_walk); + +/* begin_lockless_pgtbl_walk: Must be inserted before a function call that does + * lockless pagetable walks, such as __find_linux_pte(). + * This version is used by generic code, and always assume irqs being disabled + */ +unsigned long begin_lockless_pgtbl_walk(struct mm_struct *mm) +{ + return __begin_lockless_pgtbl_walk(mm, true); +} +EXPORT_SYMBOL(begin_lockless_pgtbl_walk); + +/* + * __end_lockless_pgtbl_walk: Must be inserted after the last use of a pointer + * returned by a lockless pagetable walk, such as __find_linux_pte() + * This version allows setting enable_irq=false, so irqs are not touched, which + * is quite useful for running when ints are already disabled (like real-mode) + */ +inline void __end_lockless_pgtbl_walk(struct mm_struct *mm, + unsigned long irq_mask, bool enable_irq) +{ + /* + * This memory barrier pairs with any code that is either trying to + * delete page tables, or split huge pages. Without this barrier, + * the page tables could be read speculatively outside of interrupt + * disabling or reference counting. + */ + smp_mb(); + + /* + * Interrupts must be disabled during the lockless page table walk. + * That's because the deleting or splitting involves flushing TLBs, + * which in turn issues interrupts, that will block when disabled. + * + * When this function is called from realmode with MSR[EE=0], + * it's not needed to touch irq, since it's already disabled. + */ + if (enable_irq) + local_irq_restore(irq_mask); + + if (IS_ENABLED(CONFIG_LOCKLESS_PAGE_TABLE_WALK_TRACKING)) + atomic_dec(&mm->lockless_pgtbl_walkers); +} +EXPORT_SYMBOL(__end_lockless_pgtbl_walk); + +/* + * end_lockless_pgtbl_walk: Must be inserted after the last use of a pointer + * returned by a lockless pagetable walk, such as __find_linux_pte() + * This version is used by generic code, and always assume irqs being enabled + */ + +void end_lockless_pgtbl_walk(struct mm_struct *mm, unsigned long irq_mask) +{ + __end_lockless_pgtbl_walk(mm, irq_mask, true); +} +EXPORT_SYMBOL(end_lockless_pgtbl_walk); + +/* + * running_lockless_pgtbl_walk: Returns the number of lockless pagetable walks + * currently running. If it returns 0, there is no running pagetable walk, and + * THP split/collapse can be safely done. This can be used to avoid more + * expensive approaches like serialize_against_pte_lookup() + */ +int running_lockless_pgtbl_walk(struct mm_struct *mm) +{ + if (IS_ENABLED(CONFIG_LOCKLESS_PAGE_TABLE_WALK_TRACKING)) + return atomic_read(&mm->lockless_pgtbl_walkers); + + /* If disabled, must return > 0, so it fallback to sync method + * (serialize_against_pte_lookup) + */ + return 1; +} +EXPORT_SYMBOL(running_lockless_pgtbl_walk); + /* * We use this to invalidate a pmdp entry before switching from a * hugepte to regular pmd entry. -- 2.20.1