On 10/25/18 11:30 AM, Souptick Joarder wrote: > On Thu, Oct 25, 2018 at 11:40 PM Florian Fainelli <[email protected]> > wrote: >> >> Some software such as perf makes unconditional use of the special >> [vectors] page which is only provided when CONFIG_KUSER_HELPERS is >> enabled in the kernel. >> >> Facilitate the debugging of such situations by printing a debug message >> to the kernel log showing the task name and the faulting address. >> >> Suggested-by: Russell King <[email protected]> >> Signed-off-by: Florian Fainelli <[email protected]> >> --- >> arch/arm/mm/fault.c | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c >> index f4ea4c62c613..f17471fbc1c4 100644 >> --- a/arch/arm/mm/fault.c >> +++ b/arch/arm/mm/fault.c >> @@ -173,6 +173,11 @@ __do_user_fault(struct task_struct *tsk, unsigned long >> addr, >> show_regs(regs); >> } >> #endif >> +#ifndef CONFIG_KUSER_HELPERS > > Just have one doubt, if the condition is "#ifdef CONFIG_KUSER_HELPER" > as commit message suggests the scenario is valid when CONFIG_KUSER_HELPER > is enabled ? No ?
#ifndef CONFIG_KUSER_HELPERS is what is intended here, when that option is not enabled, there is no [vectors] page provided in a program's virtual address space, so accesses to that virtual address will cause a fault which we are catching here. When CONFIG_KUSER_HELPERS is enabled, every program gets a valid vectors page in its virtual address space, and accessing that address would not cause a fault, since the page is there. Does this clarify the intent of this commit? > >> + if ((sig == SIGSEGV) && ((addr & PAGE_MASK) == 0xffff0000)) >> + printk(KERN_DEBUG "%s: CONFIG_KUSER_HELPERS disabled at >> 0x%08lx\n", >> + tsk->comm, addr); >> +#endif >> >> tsk->thread.address = addr; >> tsk->thread.error_code = fsr; >> -- >> 2.17.1 >> -- Florian
