linux-kernel - Re: [PATCH V4 4/8] riscv: traps: Add noinstr to prevent instrumentation inserted

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Message-ID: <CAJF2gTSs4Ycu52DH6NUzdMXQGMT51XU6x-fgQ-_OpRne+vkTqQ@mail.gmail.com>
Date:   Sat, 10 Sep 2022 17:17:44 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     arnd@...db.de, palmer@...osinc.com, tglx@...utronix.de,
        luto@...nel.org, conor.dooley@...rochip.com, heiko@...ech.de,
        jszhang@...nel.org, lazyparser@...il.com, falcon@...ylab.org,
        chenhuacai@...nel.org, apatel@...tanamicro.com,
        atishp@...shpatra.org, palmer@...belt.com,
        paul.walmsley@...ive.com, bigeasy@...utronix.de,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V4 4/8] riscv: traps: Add noinstr to prevent
 instrumentation inserted

On Thu, Sep 8, 2022 at 3:34 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Sep 07, 2022 at 10:25:02PM -0400, guoren@...nel.org wrote:
> > From: Guo Ren <guoren@...ux.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/raw
> > Suggested-by: Peter Zijlstra <peterz@...radead.org>
> > Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren@...nel.org>
> > ---
> >  arch/riscv/kernel/traps.c | 8 ++++----
> >  arch/riscv/mm/fault.c     | 2 +-
> >  2 files changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> > index 635e6ec26938..3ed3dbec250d 100644
> > --- a/arch/riscv/kernel/traps.c
> > +++ b/arch/riscv/kernel/traps.c
> > @@ -97,7 +97,7 @@ static void do_trap_error(struct pt_regs *regs, int signo, int code,
> >  #define __trap_section
> >  #endif
> >  #define DO_ERROR_INFO(name, signo, code, str)                                \
> > -asmlinkage __visible __trap_section void name(struct pt_regs *regs)  \
> > +asmlinkage __visible __trap_section void noinstr name(struct pt_regs *regs)  \
>
> But now you have __trap_section and noinstr both adding a section
> attribute.

Oops, thx for correcting. Here is my solution.

diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 635e6ec26938..eba744caa711 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -92,9 +92,11 @@ 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                                                 \
+       noinline notrace __attribute((__section__(".xip.traps")))       \
+       __no_kcsan __no_sanitize_address __no_profile __no_sanitize_coverage
 #else
-#define __trap_section
+#define __trap_section noinstr
 #endif


-- 
Best Regards
 Guo Ren