On Wed, Jan 04, 2023 at 09:40:38AM +0800, Guo Ren wrote: > On Tue, Jan 3, 2023 at 5:12 PM Alexandre Ghiti <alex@xxxxxxxx> wrote: > > > > Hi Guo, > > > > On 1/3/23 04:35, guoren@xxxxxxxxxx wrote: > > > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx> > > > > > > Without noinstr the compiler is free to insert instrumentation (think > > > all the k*SAN, KCov, GCov, ftrace etc..) which can call code we're not > > > yet ready to run this early in the entry path, for instance it could > > > rely on RCU which isn't on yet, or expect lockdep state. (by peterz) > > > > > > Link: https://lore.kernel.org/linux-riscv/YxcQ6NoPf3AH0EXe@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > > Reviewed-by: Björn Töpel <bjorn@xxxxxxxxxxxx> > > > Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > > > Tested-by: Jisheng Zhang <jszhang@xxxxxxxxxx> > > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx> > > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxx> > > > --- > > > arch/riscv/kernel/traps.c | 4 ++-- > > > arch/riscv/mm/fault.c | 2 +- > > > 2 files changed, 3 insertions(+), 3 deletions(-) > > > > > > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c > > > index 549bde5c970a..96ec76c54ff2 100644 > > > --- a/arch/riscv/kernel/traps.c > > > +++ b/arch/riscv/kernel/traps.c > > > @@ -95,9 +95,9 @@ static void do_trap_error(struct pt_regs *regs, int signo, int code, > > > } > > > > > > #if defined(CONFIG_XIP_KERNEL) && defined(CONFIG_RISCV_ALTERNATIVE) > > > -#define __trap_section __section(".xip.traps") > > > +#define __trap_section __noinstr_section(".xip.traps") > > > #else > > > -#define __trap_section > > > +#define __trap_section noinstr > > > #endif > > > #define DO_ERROR_INFO(name, signo, code, str) \ > > > asmlinkage __visible __trap_section void name(struct pt_regs *regs) \ > > > diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c > > > index d86f7cebd4a7..b26f68eac61c 100644 > > > --- a/arch/riscv/mm/fault.c > > > +++ b/arch/riscv/mm/fault.c > > > @@ -204,7 +204,7 @@ static inline bool access_error(unsigned long cause, struct vm_area_struct *vma) > > > * This routine handles page faults. It determines the address and the > > > * problem, and then passes it off to one of the appropriate routines. > > > */ > > > -asmlinkage void do_page_fault(struct pt_regs *regs) > > > +asmlinkage void noinstr do_page_fault(struct pt_regs *regs) > > > > > > (I dug the archive but can't find the series before v4, so sorry if it > > was already answered) > > > > I think we should not disable the instrumentation of those trap handlers > > as at least profiling them with ftrace would provide valuable > > information (and gcov would be nice too): why do we need to do that? A > > trap very early in the boot process is not recoverable anyway. > Everything that calls irqentry_enter() should be noinstr, and this > patch prepares for the next generic_entry convert. > > eg: > asmlinkage void noinstr do_page_fault(struct pt_regs *regs) > { > irqentry_state_t state = irqentry_enter(regs); > > __do_page_fault(regs); > > local_irq_disable(); > > irqentry_exit(regs, state); > } > NOKPROBE_SYMBOL(do_page_fault); > > You still could profile __do_page_fault. > > > > > And I took a look at other architectures, none of them disables the > > instrumentation on do_page_fault. > That's not true, have a look at power & arm64. All of them have some > limitations at the entry of page_fault. Well, arm64's can't be kprobed, but is *can* be traced with ftrace, and *can* be instrumented with KASAN and friends. I'm not sure that we actually need to inhibit kprobes for do_page_fault, and we might be able to relax that. As a general thing, we've tried to centralize all the necesarily-noinstr bits in arch/arm64/kernel/entry-common.c, and keep everything else as instrumentable as possible. I'd recommend doing similar, and have a central file for any entry bits which can't live in the generic entry code, and keep the rest instrumentable. That will make it easier to maintain and verify. Thanks, Mark.
