Messages in this thread Patch in this message | | | Subject | Re: [PATCH] x86: Add a list for custom page fault handlers. | From | Harvey Harrison <> | Date | Tue, 29 Jan 2008 18:28:22 -0800 |
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From: Pekka Paalanen <pq@iki.fi>
Provides kernel modules a way to register custom page fault handlers. On every page fault, except those handled in vmalloc_fault(), this will call a list of registered functions. The functions may handle the fault and force do_page_fault() to return immediately.
This functionality is similar to the now removed page fault notifiers. Custom page fault handlers are used by debugging and reverse engineering tools. Mmio-trace is one such tool and a patch to add it into the tree will follow.
The custom page fault handlers are called from the exact same points in do_page_fault() as the page fault notifiers were.
Signed-off-by: Pekka Paalanen <pq@iki.fi> Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com> --- Ingo, ported Pekka's patch to current x86.git for review. I have not incorporated the RCU comments from Peter Zjistra, but I have folded some of the static functions into on handle_custom_pf function that will match the handle_kprobe_fault helper that will be ready for RC1.
Harvey
arch/x86/Kconfig.debug | 9 ++++++++ arch/x86/mm/fault.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 60 insertions(+), 0 deletions(-)
diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug index 2e1e3af..9b44bc5 100644 --- a/arch/x86/Kconfig.debug +++ b/arch/x86/Kconfig.debug @@ -225,4 +225,13 @@ config CPA_DEBUG help Do change_page_attr self tests at boot. +config PAGE_FAULT_HANDLERS + bool "Custom page fault handlers" + depends on DEBUG_KERNEL + help + Allow the use of custom page fault handlers. A kernel module may + register a function that is called on every page fault not handled + for vmalloc. Custom handlers are used by some debugging and reverse + engineering tools. + endmenu diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index e28cc52..c6c8164 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -49,6 +49,54 @@ #define PF_RSVD (1<<3) #define PF_INSTR (1<<4) +#ifdef CONFIG_PAGE_FAULT_HANDLERS +static HLIST_HEAD(pf_handlers); /* protected by RCU */ +static DEFINE_SPINLOCK(pf_handlers_writer); + +void register_page_fault_handler(struct pf_handler *new_pfh) +{ + spin_lock(&pf_handlers_writer); + hlist_add_head_rcu(&new_pfh->hlist, &pf_handlers); + spin_unlock(&pf_handlers_writer); +} +EXPORT_SYMBOL_GPL(register_page_fault_handler); + +void unregister_page_fault_handler(struct pf_handler *old_pfh) +{ + might_sleep(); + spin_lock(&pf_handlers_writer); + hlist_del_rcu(&old_pfh->hlist); + spin_unlock(&pf_handlers_writer); + synchronize_rcu(); +} +EXPORT_SYMBOL_GPL(unregister_page_fault_handler); +#endif + +/* returns non-zero if do_page_fault() should return */ +static int handle_custom_pf(struct pt_regs *regs, unsigned long error_code, + unsigned long address) +{ +#ifdef CONFIG_PAGE_FAULT_HANDLERS + int ret = 0; + struct pf_handler *cur; + struct hlist_node *ncur; + + if (hlist_empty(&pf_handlers)) + return 0; + + rcu_read_lock(); + hlist_for_each_entry_rcu(cur, ncur, &pf_handlers, hlist) { + ret = cur->handler(regs, error_code, address); + if (ret) + break; + } + rcu_read_unlock(); + return ret; +#else + return 0; +#endif +} + static inline int notify_page_fault(struct pt_regs *regs) { #ifdef CONFIG_KPROBES @@ -588,6 +636,9 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code) if (notify_page_fault(regs)) return; + if (handle_custom_pf(regs, error_code, address)) + return; + /* * We fault-in kernel-space virtual memory on-demand. The * 'reference' page table is init_mm.pgd. -- 1.5.4.rc4.1142.gf5a97
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