From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christophe Leroy Date: Tue, 11 Jun 2019 04:46:52 +0000 Subject: Re: [RFC V3] mm: Generalize and rename notify_page_fault() as kprobe_page_fault() Message-Id: List-Id: References: <1559903655-5609-1-git-send-email-anshuman.khandual@arm.com> <97e9c9b3-89c8-d378-4730-841a900e6800@arm.com> In-Reply-To: <97e9c9b3-89c8-d378-4730-841a900e6800@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: Anshuman Khandual , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Mark Rutland , Michal Hocko , linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Peter Zijlstra , Catalin Marinas , Dave Hansen , Heiko Carstens , Paul Mackerras , Matthew Wilcox , sparclinux@vger.kernel.org, linux-s390@vger.kernel.org, Yoshinori Sato , Michael Ellerman , x86@kernel.org, Russell King , Will Deacon , Ingo Molnar , Fenghua Yu , Stephen Rothwell , Andrey Konovalov , Andy Lutomirski , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Tony Luck , Martin Schwidefsky , Andrew Morton , linuxppc-dev@lists.ozlabs.org, "David S. Miller" Le 10/06/2019 à 04:39, Anshuman Khandual a écrit : > > > On 06/07/2019 09:01 PM, Christophe Leroy wrote: >> >> >> Le 07/06/2019 à 12:34, Anshuman Khandual a écrit : >>> 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. >>> >>> kprobes_built_in() can detect CONFIG_KPROBES, hence new kprobe_page_fault() >>> need not be wrapped again within CONFIG_KPROBES. Trap number argument can >>> now contain upto an 'unsigned int' accommodating all possible platforms. >>> >>> kprobe_page_fault() goes the x86 way while dealing with preemption context. >>> As explained in these following commits the invoking context in itself must >>> be non-preemptible for kprobes processing context irrespective of whether >>> kprobe_running() or perhaps smp_processor_id() is safe or not. It does not >>> make much sense to continue when original context is preemptible. Instead >>> just bail out earlier. >>> >>> commit a980c0ef9f6d >>> ("x86/kprobes: Refactor kprobes_fault() like kprobe_exceptions_notify()") >>> >>> commit b506a9d08bae ("x86: code clarification patch to Kprobes arch code") >>> >>> Cc: linux-arm-kernel@lists.infradead.org >>> Cc: linux-ia64@vger.kernel.org >>> Cc: linuxppc-dev@lists.ozlabs.org >>> Cc: linux-s390@vger.kernel.org >>> Cc: linux-sh@vger.kernel.org >>> Cc: sparclinux@vger.kernel.org >>> Cc: x86@kernel.org >>> Cc: Andrew Morton >>> Cc: Michal Hocko >>> Cc: Matthew Wilcox >>> Cc: Mark Rutland >>> Cc: Christophe Leroy >>> Cc: Stephen Rothwell >>> Cc: Andrey Konovalov >>> Cc: Michael Ellerman >>> Cc: Paul Mackerras >>> Cc: Russell King >>> Cc: Catalin Marinas >>> Cc: Will Deacon >>> Cc: Tony Luck >>> Cc: Fenghua Yu >>> Cc: Martin Schwidefsky >>> Cc: Heiko Carstens >>> Cc: Yoshinori Sato >>> Cc: "David S. Miller" >>> Cc: Thomas Gleixner >>> Cc: Peter Zijlstra >>> Cc: Ingo Molnar >>> Cc: Andy Lutomirski >>> Cc: Dave Hansen >>> >>> Signed-off-by: Anshuman Khandual >>> --- >>> Testing: >>> >>> - Build and boot tested on arm64 and x86 >>> - Build tested on some other archs (arm, sparc64, alpha, powerpc etc) >>> >>> Changes in RFC V3: >>> >>> - Updated the commit message with an explaination for new preemption behaviour >>> - Moved notify_page_fault() to kprobes.h with 'static nokprobe_inline' per Matthew >>> - Changed notify_page_fault() return type from int to bool per Michael Ellerman >>> - Renamed notify_page_fault() as kprobe_page_fault() per Peterz >>> >>> Changes in RFC V2: (https://patchwork.kernel.org/patch/10974221/) >>> >>> - Changed generic notify_page_fault() per Mathew Wilcox >>> - Changed x86 to use new generic notify_page_fault() >>> - s/must not/need not/ in commit message per Matthew Wilcox >>> >>> Changes in RFC V1: (https://patchwork.kernel.org/patch/10968273/) >>> >>>   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 ++++++++++++++++ >>>   9 files changed, 27 insertions(+), 155 deletions(-) >>> >> >> [...] >> >>> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h >>> index 443d980..064dd15 100644 >>> --- a/include/linux/kprobes.h >>> +++ 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; >> >> ret is pointless. >> >>> + >>> +    /* >>> +     * 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)) >> >> don't need an 'if A if B', can do 'if A && B' > > Which will make it a very lengthy condition check. Yes. But is that a problem at all ? For me the following would be easier to read. if (kprobes_built_in() && !preemptible() && !user_mode(regs) && kprobe_running() && kprobe_fault_handler(regs, trap)) ret = 1; Christophe > >> >>> +            ret = 1; >> >> can do 'return true;' directly here >> >>> +    } >>> +    return ret; >> >> And 'return false' here. > > Makes sense, will drop ret. >