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[217.140.110.172]) by mx.google.com with ESMTP id g44si175002edg.58.2019.06.09.21.34.44 for ; Sun, 09 Jun 2019 21:34:44 -0700 (PDT) Received-SPF: pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) client-ip=217.140.110.172; Authentication-Results: mx.google.com; spf=pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 69043337; Sun, 9 Jun 2019 21:34:43 -0700 (PDT) Received: from [10.162.42.131] (p8cg001049571a15.blr.arm.com [10.162.42.131]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B2CA33F557; Sun, 9 Jun 2019 21:34:31 -0700 (PDT) Subject: Re: [RFC V3] mm: Generalize and rename notify_page_fault() as kprobe_page_fault() To: Matthew Wilcox Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, x86@kernel.org, Andrew Morton , Michal Hocko , Mark Rutland , Christophe Leroy , Stephen Rothwell , Andrey Konovalov , Michael Ellerman , Paul Mackerras , Russell King , Catalin Marinas , Will Deacon , Tony Luck , Fenghua Yu , Martin Schwidefsky , Heiko Carstens , Yoshinori Sato , "David S. Miller" , Thomas Gleixner , Peter Zijlstra , Ingo Molnar , Andy Lutomirski , Dave Hansen , Vineet Gupta , linux-snps-arc@lists.infradead.org, James Hogan , linux-mips@vger.kernel.org, Ralf Baechle , Paul Burton References: <1559903655-5609-1-git-send-email-anshuman.khandual@arm.com> <20190607201202.GA32656@bombadil.infradead.org> From: Anshuman Khandual Message-ID: Date: Mon, 10 Jun 2019 10:04:49 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190607201202.GA32656@bombadil.infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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: On 06/08/2019 01:42 AM, Matthew Wilcox wrote: > Before: > >> @@ -46,23 +46,6 @@ kmmio_fault(struct pt_regs *regs, unsigned long addr) >> return 0; >> } >> >> -static nokprobe_inline int kprobes_fault(struct pt_regs *regs) >> -{ >> - if (!kprobes_built_in()) >> - return 0; >> - if (user_mode(regs)) >> - return 0; >> - /* >> - * To be potentially processing a kprobe fault and to be allowed to call >> - * kprobe_running(), we have to be non-preemptible. >> - */ >> - if (preemptible()) >> - return 0; >> - if (!kprobe_running()) >> - return 0; >> - return kprobe_fault_handler(regs, X86_TRAP_PF); >> -} > > After: > >> +++ b/include/linux/kprobes.h >> @@ -458,4 +458,20 @@ static inline bool is_kprobe_optinsn_slot(unsigned long addr) >> } >> #endif >> >> +static nokprobe_inline bool kprobe_page_fault(struct pt_regs *regs, >> + unsigned int trap) >> +{ >> + int ret = 0; >> + >> + /* >> + * To be potentially processing a kprobe fault and to be allowed >> + * to call kprobe_running(), we have to be non-preemptible. >> + */ >> + if (kprobes_built_in() && !preemptible() && !user_mode(regs)) { >> + if (kprobe_running() && kprobe_fault_handler(regs, trap)) >> + ret = 1; >> + } >> + return ret; >> +} > > Do you really think this is easier to read? > > Why not just move the x86 version to include/linux/kprobes.h, and replace > the int with bool? Will just return bool directly without an additional variable here as suggested before. But for the conditional statement, I guess the proposed one here is more compact than the x86 one. > > On Fri, Jun 07, 2019 at 04:04:15PM +0530, Anshuman Khandual wrote: >> Very similar definitions for notify_page_fault() are being used by multiple >> architectures duplicating much of the same code. This attempts to unify all >> of them into a generic implementation, rename it as kprobe_page_fault() and >> then move it to a common header. > > I think this description suffers from having been written for v1 of > this patch. It describes what you _did_, but it's not what this patch > currently _is_. > > Why not something like: > > Architectures which support kprobes have very similar boilerplate around > calling kprobe_fault_handler(). Use a helper function in kprobes.h to > unify them, based on the x86 code. > > This changes the behaviour for other architectures when preemption > is enabled. Previously, they would have disabled preemption while > calling the kprobe handler. However, preemption would be disabled > if this fault was due to a kprobe, so we know the fault was not due > to a kprobe handler and can simply return failure. This behaviour was > introduced in commit a980c0ef9f6d ("x86/kprobes: Refactor kprobes_fault() > like kprobe_exceptions_notify()") Will replace commit message with above. > >> arch/arm/mm/fault.c | 24 +----------------------- >> arch/arm64/mm/fault.c | 24 +----------------------- >> arch/ia64/mm/fault.c | 24 +----------------------- >> arch/powerpc/mm/fault.c | 23 ++--------------------- >> arch/s390/mm/fault.c | 16 +--------------- >> arch/sh/mm/fault.c | 18 ++---------------- >> arch/sparc/mm/fault_64.c | 16 +--------------- >> arch/x86/mm/fault.c | 21 ++------------------- >> include/linux/kprobes.h | 16 ++++++++++++++++ > > What about arc and mips? + Vineet Gupta + linux-snps-arc@lists.infradead.org + James Hogan + Paul Burton + Ralf Baechle + linux-mips@vger.kernel.org Both the above architectures dont call kprobe_fault_handler() from the page fault context (do_page_fault() to be specific). Though it gets called from mips kprobe_exceptions_notify (DIE_PAGE_FAULT). Am I missing something here ?