Messages in this thread | | | Subject | Re: [RFC V3] mm: Generalize and rename notify_page_fault() as kprobe_page_fault() | From | Christophe Leroy <> | Date | Tue, 11 Jun 2019 06:46:52 +0200 |
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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 <akpm@linux-foundation.org> >>> Cc: Michal Hocko <mhocko@suse.com> >>> Cc: Matthew Wilcox <willy@infradead.org> >>> Cc: Mark Rutland <mark.rutland@arm.com> >>> Cc: Christophe Leroy <christophe.leroy@c-s.fr> >>> Cc: Stephen Rothwell <sfr@canb.auug.org.au> >>> Cc: Andrey Konovalov <andreyknvl@google.com> >>> Cc: Michael Ellerman <mpe@ellerman.id.au> >>> Cc: Paul Mackerras <paulus@samba.org> >>> Cc: Russell King <linux@armlinux.org.uk> >>> Cc: Catalin Marinas <catalin.marinas@arm.com> >>> Cc: Will Deacon <will.deacon@arm.com> >>> Cc: Tony Luck <tony.luck@intel.com> >>> Cc: Fenghua Yu <fenghua.yu@intel.com> >>> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> >>> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> >>> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> >>> Cc: "David S. Miller" <davem@davemloft.net> >>> Cc: Thomas Gleixner <tglx@linutronix.de> >>> Cc: Peter Zijlstra <peterz@infradead.org> >>> Cc: Ingo Molnar <mingo@redhat.com> >>> Cc: Andy Lutomirski <luto@kernel.org> >>> Cc: Dave Hansen <dave.hansen@linux.intel.com> >>> >>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >>> --- >>> 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. >
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