From: Guo Ren <guoren@kernel.org>
To: Alexandre Ghiti <alex@ghiti.fr>
Cc: arnd@arndb.de, palmer@rivosinc.com, tglx@linutronix.de,
peterz@infradead.org, luto@kernel.org,
conor.dooley@microchip.com, heiko@sntech.de, jszhang@kernel.org,
lazyparser@gmail.com, falcon@tinylab.org, chenhuacai@kernel.org,
apatel@ventanamicro.com, atishp@atishpatra.org,
mark.rutland@arm.com, ben@decadent.org.uk, bjorn@kernel.org,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-riscv@lists.infradead.org,
"Guo Ren" <guoren@linux.alibaba.com>,
"Björn Töpel" <bjorn@rivosinc.com>
Subject: Re: [PATCH -next V12 3/7] riscv: entry: Add noinstr to prevent instrumentation inserted
Date: Wed, 4 Jan 2023 09:40:38 +0800 [thread overview]
Message-ID: <CAJF2gTTSretKkJGNV7Y6iJboPuAWUQ=to=RPA8_-Nz8dnufGAg@mail.gmail.com> (raw)
In-Reply-To: <36314eb6-e41d-30b9-9ac4-12b88a108b7b@ghiti.fr>
On Tue, Jan 3, 2023 at 5:12 PM Alexandre Ghiti <alex@ghiti.fr> wrote:
>
> Hi Guo,
>
> On 1/3/23 04:35, guoren@kernel.org wrote:
> > From: Guo Ren <guoren@linux.alibaba.com>
> >
> > 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@hirez.programming.kicks-ass.net/
> > Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
> > Suggested-by: Peter Zijlstra <peterz@infradead.org>
> > Tested-by: Jisheng Zhang <jszhang@kernel.org>
> > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren@kernel.org>
> > ---
> > 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.
>
>
> > {
> > struct task_struct *tsk;
> > struct vm_area_struct *vma;
--
Best Regards
Guo Ren
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next prev parent reply other threads:[~2023-01-04 1:41 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-03 3:35 [PATCH -next V12 0/7] riscv: Add GENERIC_ENTRY support guoren
2023-01-03 3:35 ` [PATCH -next V12 1/7] compiler_types.h: Add __noinstr_section() for noinstr guoren
2023-01-03 3:35 ` [PATCH -next V12 2/7] riscv: ptrace: Remove duplicate operation guoren
2023-01-03 3:35 ` [PATCH -next V12 3/7] riscv: entry: Add noinstr to prevent instrumentation inserted guoren
2023-01-03 9:11 ` Alexandre Ghiti
2023-01-04 1:40 ` Guo Ren [this message]
2023-01-04 12:03 ` Mark Rutland
2023-01-07 11:48 ` Guo Ren
2023-01-04 11:55 ` Mark Rutland
2023-01-07 11:49 ` Guo Ren
2023-01-03 3:35 ` [PATCH -next V12 4/7] riscv: entry: Convert to generic entry guoren
2023-01-03 3:35 ` [PATCH -next V12 5/7] riscv: entry: Remove extra level wrappers of trace_hardirqs_{on,off} guoren
2023-01-03 3:35 ` [PATCH -next V12 6/7] riscv: entry: Consolidate ret_from_kernel_thread into ret_from_fork guoren
2023-01-03 3:35 ` [PATCH -next V12 7/7] riscv: entry: Consolidate general regs saving/restoring guoren
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