| Message ID | 1559195713-6956-1-git-send-email-anshuman.khandual@arm.com (mailing list archive) |
|---|---|
| State | RFC |
| Headers | show |
| Series | [RFC] mm: Generalize notify_page_fault() | expand |
On Thu, May 30, 2019 at 11:25:13AM +0530, Anshuman Khandual wrote: > Similar notify_page_fault() definitions are being used by architectures > duplicating much of the same code. This attempts to unify them into a > single implementation, generalize it and then move it to a common place. > kprobes_built_in() can detect CONFIG_KPROBES, hence notify_page_fault() > must not be wrapped again within CONFIG_KPROBES. Trap number argument can This is a funny quirk of the English language. "must not" means "is not allowed to be", not "does not have to be". > @@ -141,6 +142,19 @@ static int __init init_zero_pfn(void) > core_initcall(init_zero_pfn); > > > +int __kprobes notify_page_fault(struct pt_regs *regs, unsigned int trap) > +{ > + int ret = 0; > + > + if (kprobes_built_in() && !user_mode(regs)) { > + preempt_disable(); > + if (kprobe_running() && kprobe_fault_handler(regs, trap)) > + ret = 1; > + preempt_enable(); > + } > + return ret; > +} > + > #if defined(SPLIT_RSS_COUNTING) Comparing this to the canonical implementation (ie x86), it looks similar. 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); } The two handle preemption differently. Why is x86 wrong and this one correct?
On 05/30/2019 04:36 PM, Matthew Wilcox wrote: > On Thu, May 30, 2019 at 11:25:13AM +0530, Anshuman Khandual wrote: >> Similar notify_page_fault() definitions are being used by architectures >> duplicating much of the same code. This attempts to unify them into a >> single implementation, generalize it and then move it to a common place. >> kprobes_built_in() can detect CONFIG_KPROBES, hence notify_page_fault() >> must not be wrapped again within CONFIG_KPROBES. Trap number argument can > > This is a funny quirk of the English language. "must not" means "is not > allowed to be", not "does not have to be". You are right. Noted for future. Thanks ! > >> @@ -141,6 +142,19 @@ static int __init init_zero_pfn(void) >> core_initcall(init_zero_pfn); >> >> >> +int __kprobes notify_page_fault(struct pt_regs *regs, unsigned int trap) >> +{ >> + int ret = 0; >> + >> + if (kprobes_built_in() && !user_mode(regs)) { >> + preempt_disable(); >> + if (kprobe_running() && kprobe_fault_handler(regs, trap)) >> + ret = 1; >> + preempt_enable(); >> + } >> + return ret; >> +} >> + >> #if defined(SPLIT_RSS_COUNTING) > > Comparing this to the canonical implementation (ie x86), it looks similar. > > 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); > } > > The two handle preemption differently. Why is x86 wrong and this one > correct? Here it expects context to be already non-preemptible where as the proposed generic function makes it non-preemptible with a preempt_[disable|enable]() pair for the required code section, irrespective of it's present state. Is not this better ?
On Thu, May 30, 2019 at 05:31:15PM +0530, Anshuman Khandual wrote: > On 05/30/2019 04:36 PM, Matthew Wilcox wrote: > > The two handle preemption differently. Why is x86 wrong and this one > > correct? > > Here it expects context to be already non-preemptible where as the proposed > generic function makes it non-preemptible with a preempt_[disable|enable]() > pair for the required code section, irrespective of it's present state. Is > not this better ? git log -p arch/x86/mm/fault.c search for 'kprobes'. tell me what you think.
On 05/30/2019 07:09 PM, Matthew Wilcox wrote: > On Thu, May 30, 2019 at 05:31:15PM +0530, Anshuman Khandual wrote: >> On 05/30/2019 04:36 PM, Matthew Wilcox wrote: >>> The two handle preemption differently. Why is x86 wrong and this one >>> correct? >> >> Here it expects context to be already non-preemptible where as the proposed >> generic function makes it non-preemptible with a preempt_[disable|enable]() >> pair for the required code section, irrespective of it's present state. Is >> not this better ? > > git log -p arch/x86/mm/fault.c > > search for 'kprobes'. > > tell me what you think. > Are you referring to these following commits a980c0ef9f6d ("x86/kprobes: Refactor kprobes_fault() like kprobe_exceptions_notify()") b506a9d08bae ("x86: code clarification patch to Kprobes arch code") In particular the later one (b506a9d08bae). It explains how the invoking context in itself should be non-preemptible for the kprobes processing context irrespective of whether kprobe_running() or perhaps smp_processor_id() is safe or not. Hence it does not make much sense to continue when original invoking context is preemptible. Instead just bail out earlier. This seems to be making more sense than preempt disable-enable pair. If there are no concerns about this change from other platforms, I will change the preemption behavior in proposed generic function next time around.
On Fri, May 31, 2019 at 02:17:43PM +0530, Anshuman Khandual wrote: > On 05/30/2019 07:09 PM, Matthew Wilcox wrote: > > On Thu, May 30, 2019 at 05:31:15PM +0530, Anshuman Khandual wrote: > >> On 05/30/2019 04:36 PM, Matthew Wilcox wrote: > >>> The two handle preemption differently. Why is x86 wrong and this one > >>> correct? > >> > >> Here it expects context to be already non-preemptible where as the proposed > >> generic function makes it non-preemptible with a preempt_[disable|enable]() > >> pair for the required code section, irrespective of it's present state. Is > >> not this better ? > > > > git log -p arch/x86/mm/fault.c > > > > search for 'kprobes'. > > > > tell me what you think. > > Are you referring to these following commits > > a980c0ef9f6d ("x86/kprobes: Refactor kprobes_fault() like kprobe_exceptions_notify()") > b506a9d08bae ("x86: code clarification patch to Kprobes arch code") > > In particular the later one (b506a9d08bae). It explains how the invoking context > in itself should be non-preemptible for the kprobes processing context irrespective > of whether kprobe_running() or perhaps smp_processor_id() is safe or not. Hence it > does not make much sense to continue when original invoking context is preemptible. > Instead just bail out earlier. This seems to be making more sense than preempt > disable-enable pair. If there are no concerns about this change from other platforms, > I will change the preemption behavior in proposed generic function next time around. Exactly. So, any of the arch maintainers know of a reason they behave differently from x86 in this regard? Or can Anshuman use the x86 implementation for all the architectures supporting kprobes?
On 05/31/2019 11:18 PM, Matthew Wilcox wrote: > On Fri, May 31, 2019 at 02:17:43PM +0530, Anshuman Khandual wrote: >> On 05/30/2019 07:09 PM, Matthew Wilcox wrote: >>> On Thu, May 30, 2019 at 05:31:15PM +0530, Anshuman Khandual wrote: >>>> On 05/30/2019 04:36 PM, Matthew Wilcox wrote: >>>>> The two handle preemption differently. Why is x86 wrong and this one >>>>> correct? >>>> >>>> Here it expects context to be already non-preemptible where as the proposed >>>> generic function makes it non-preemptible with a preempt_[disable|enable]() >>>> pair for the required code section, irrespective of it's present state. Is >>>> not this better ? >>> >>> git log -p arch/x86/mm/fault.c >>> >>> search for 'kprobes'. >>> >>> tell me what you think. >> >> Are you referring to these following commits >> >> a980c0ef9f6d ("x86/kprobes: Refactor kprobes_fault() like kprobe_exceptions_notify()") >> b506a9d08bae ("x86: code clarification patch to Kprobes arch code") >> >> In particular the later one (b506a9d08bae). It explains how the invoking context >> in itself should be non-preemptible for the kprobes processing context irrespective >> of whether kprobe_running() or perhaps smp_processor_id() is safe or not. Hence it >> does not make much sense to continue when original invoking context is preemptible. >> Instead just bail out earlier. This seems to be making more sense than preempt >> disable-enable pair. If there are no concerns about this change from other platforms, >> I will change the preemption behavior in proposed generic function next time around. > > Exactly. > > So, any of the arch maintainers know of a reason they behave differently > from x86 in this regard? Or can Anshuman use the x86 implementation > for all the architectures supporting kprobes? So the generic notify_page_fault() will be like this. int __kprobes notify_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; }
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c index 58f69fa..1bc3b18 100644 --- a/arch/arm/mm/fault.c +++ b/arch/arm/mm/fault.c @@ -30,28 +30,6 @@ #ifdef CONFIG_MMU -#ifdef CONFIG_KPROBES -static inline int notify_page_fault(struct pt_regs *regs, unsigned int fsr) -{ - int ret = 0; - - if (!user_mode(regs)) { - /* kprobe_running() needs smp_processor_id() */ - preempt_disable(); - if (kprobe_running() && kprobe_fault_handler(regs, fsr)) - ret = 1; - preempt_enable(); - } - - return ret; -} -#else -static inline int notify_page_fault(struct pt_regs *regs, unsigned int fsr) -{ - return 0; -} -#endif - /* * This is useful to dump out the page tables associated with * 'addr' in mm 'mm'. diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index a30818e..152f1f1 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -70,28 +70,6 @@ static inline const struct fault_info *esr_to_debug_fault_info(unsigned int esr) return debug_fault_info + DBG_ESR_EVT(esr); } -#ifdef CONFIG_KPROBES -static inline int notify_page_fault(struct pt_regs *regs, unsigned int esr) -{ - int ret = 0; - - /* kprobe_running() needs smp_processor_id() */ - if (!user_mode(regs)) { - preempt_disable(); - if (kprobe_running() && kprobe_fault_handler(regs, esr)) - ret = 1; - preempt_enable(); - } - - return ret; -} -#else -static inline int notify_page_fault(struct pt_regs *regs, unsigned int esr) -{ - return 0; -} -#endif - static void data_abort_decode(unsigned int esr) { pr_alert("Data abort info:\n"); diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c index 5baeb02..64283d2 100644 --- a/arch/ia64/mm/fault.c +++ b/arch/ia64/mm/fault.c @@ -21,28 +21,6 @@ extern int die(char *, struct pt_regs *, long); -#ifdef CONFIG_KPROBES -static inline int notify_page_fault(struct pt_regs *regs, int trap) -{ - int ret = 0; - - if (!user_mode(regs)) { - /* kprobe_running() needs smp_processor_id() */ - preempt_disable(); - if (kprobe_running() && kprobe_fault_handler(regs, trap)) - ret = 1; - preempt_enable(); - } - - return ret; -} -#else -static inline int notify_page_fault(struct pt_regs *regs, int trap) -{ - return 0; -} -#endif - /* * Return TRUE if ADDRESS points at a page in the kernel's mapped segment * (inside region 5, on ia64) and that page is present. diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c index b5d3578..5a0d71f 100644 --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -46,26 +46,6 @@ #include <asm/debug.h> #include <asm/kup.h> -static inline bool notify_page_fault(struct pt_regs *regs) -{ - bool ret = false; - -#ifdef CONFIG_KPROBES - /* kprobe_running() needs smp_processor_id() */ - if (!user_mode(regs)) { - preempt_disable(); - if (kprobe_running() && kprobe_fault_handler(regs, 11)) - ret = true; - preempt_enable(); - } -#endif /* CONFIG_KPROBES */ - - if (unlikely(debugger_fault_handler(regs))) - ret = true; - - return ret; -} - /* * Check whether the instruction inst is a store using * an update addressing form which will update r1. @@ -466,8 +446,9 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address, int is_write = page_fault_is_write(error_code); vm_fault_t fault, major = 0; bool must_retry = false; + int kprobe_fault = notify_page_fault(regs, 11); - if (notify_page_fault(regs)) + if (unlikely(debugger_fault_handler(regs) || kprobe_fault)) return 0; if (unlikely(page_fault_is_bad(error_code))) { diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c index c220399..d317263 100644 --- a/arch/s390/mm/fault.c +++ b/arch/s390/mm/fault.c @@ -67,20 +67,6 @@ static int __init fault_init(void) } early_initcall(fault_init); -static inline int notify_page_fault(struct pt_regs *regs) -{ - int ret = 0; - - /* kprobe_running() needs smp_processor_id() */ - if (kprobes_built_in() && !user_mode(regs)) { - preempt_disable(); - if (kprobe_running() && kprobe_fault_handler(regs, 14)) - ret = 1; - preempt_enable(); - } - return ret; -} - /* * Find out which address space caused the exception. * Access register mode is impossible, ignore space == 3. @@ -409,7 +395,7 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access) */ clear_pt_regs_flag(regs, PIF_PER_TRAP); - if (notify_page_fault(regs)) + if (notify_page_fault(regs, 14)) return 0; mm = tsk->mm; diff --git a/arch/sh/mm/fault.c b/arch/sh/mm/fault.c index 6defd2c6..94bdfcb 100644 --- a/arch/sh/mm/fault.c +++ b/arch/sh/mm/fault.c @@ -24,20 +24,6 @@ #include <asm/tlbflush.h> #include <asm/traps.h> -static inline int notify_page_fault(struct pt_regs *regs, int trap) -{ - int ret = 0; - - if (kprobes_built_in() && !user_mode(regs)) { - preempt_disable(); - if (kprobe_running() && kprobe_fault_handler(regs, trap)) - ret = 1; - preempt_enable(); - } - - return ret; -} - static void force_sig_info_fault(int si_signo, int si_code, unsigned long address, struct task_struct *tsk) diff --git a/arch/sparc/mm/fault_64.c b/arch/sparc/mm/fault_64.c index 8f8a604..e5557a1 100644 --- a/arch/sparc/mm/fault_64.c +++ b/arch/sparc/mm/fault_64.c @@ -38,20 +38,6 @@ int show_unhandled_signals = 1; -static inline __kprobes int notify_page_fault(struct pt_regs *regs) -{ - int ret = 0; - - /* kprobe_running() needs smp_processor_id() */ - if (kprobes_built_in() && !user_mode(regs)) { - preempt_disable(); - if (kprobe_running() && kprobe_fault_handler(regs, 0)) - ret = 1; - preempt_enable(); - } - return ret; -} - static void __kprobes unhandled_fault(unsigned long address, struct task_struct *tsk, struct pt_regs *regs) @@ -285,7 +271,7 @@ asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs) fault_code = get_thread_fault_code(); - if (notify_page_fault(regs)) + if (notify_page_fault(regs, 0)) goto exit_exception; si_code = SEGV_MAPERR; diff --git a/include/linux/mm.h b/include/linux/mm.h index 0e8834a..c5a8dcf 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1778,6 +1778,7 @@ static inline int pte_devmap(pte_t pte) } #endif +int notify_page_fault(struct pt_regs *regs, unsigned int trap); int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot); extern pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr, diff --git a/mm/memory.c b/mm/memory.c index ddf20bd..82022d7 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -52,6 +52,7 @@ #include <linux/pagemap.h> #include <linux/memremap.h> #include <linux/ksm.h> +#include <linux/kprobes.h> #include <linux/rmap.h> #include <linux/export.h> #include <linux/delayacct.h> @@ -141,6 +142,19 @@ static int __init init_zero_pfn(void) core_initcall(init_zero_pfn); +int __kprobes notify_page_fault(struct pt_regs *regs, unsigned int trap) +{ + int ret = 0; + + if (kprobes_built_in() && !user_mode(regs)) { + preempt_disable(); + if (kprobe_running() && kprobe_fault_handler(regs, trap)) + ret = 1; + preempt_enable(); + } + return ret; +} + #if defined(SPLIT_RSS_COUNTING) void sync_mm_rss(struct mm_struct *mm)
Similar notify_page_fault() definitions are being used by architectures duplicating much of the same code. This attempts to unify them into a single implementation, generalize it and then move it to a common place. kprobes_built_in() can detect CONFIG_KPROBES, hence notify_page_fault() must not be wrapped again within CONFIG_KPROBES. Trap number argument can now contain upto an 'unsigned int' accommodating all possible platforms. Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> 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: 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> --- Boot tested on arm64 and build tested on some others. arch/arm/mm/fault.c | 22 ---------------------- arch/arm64/mm/fault.c | 22 ---------------------- arch/ia64/mm/fault.c | 22 ---------------------- arch/powerpc/mm/fault.c | 23 ++--------------------- arch/s390/mm/fault.c | 16 +--------------- arch/sh/mm/fault.c | 14 -------------- arch/sparc/mm/fault_64.c | 16 +--------------- include/linux/mm.h | 1 + mm/memory.c | 14 ++++++++++++++ 9 files changed, 19 insertions(+), 131 deletions(-)