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From: Mark Rutland <mark.rutland@arm.com>
To: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com,
	james.morse@arm.com, joey.gouly@arm.com, maz@kernel.org
Subject: Re: [PATCH v3 19/20] arm64: entry: don't instrument entry code with KCOV
Date: Fri, 4 Jun 2021 18:49:50 +0100	[thread overview]
Message-ID: <20210604174950.GD73426@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20210604171628.GE3416@willie-the-truck>

On Fri, Jun 04, 2021 at 06:16:28PM +0100, Will Deacon wrote:
> On Tue, May 25, 2021 at 07:33:01PM +0100, Mark Rutland wrote:
> > The code in entry-common.c runs at exception entry and return
> > boundaries, where portions of the kernel environment aren't available.
> > For example, RCU may not be watching, and lockdep state may be
> > out-of-sync with the hardware. Due to this, it is not sound to
> > instrument this code.
> > 
> > We generally avoid instrumentation by marking the entry functions as
> > `noinstr`, but currently this doesn't inhibit KCOV instrumentation.
> > Prevent this by disabling KCOV for the entire compilation unit.
> > 
> > Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: James Morse <james.morse@arm.com>
> > Cc: Marc Zyngier <maz@kernel.org>
> > Cc: Will Deacon <will@kernel.org>
> > ---
> >  arch/arm64/kernel/Makefile | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> > index 6cc97730790e..294063032428 100644
> > --- a/arch/arm64/kernel/Makefile
> > +++ b/arch/arm64/kernel/Makefile
> > @@ -14,6 +14,8 @@ CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE)
> >  CFLAGS_REMOVE_syscall.o	 = -fstack-protector -fstack-protector-strong
> >  CFLAGS_syscall.o	+= -fno-stack-protector
> 
> Can you stick a comment here please? Just summarising what you have in the
> commit message would be handy.

Sure; I've added:

# It's not safe to invoke KCOV when portions of the kernel environment aren't
# available or are out-of-sync with HW state. Since `noinstr` doesn't always
# inhibit KCOV instrumentation, disable it for the entire compilation unit.

... since that will also cover the idle.o case in the next patch.

Thanks,
Mark.

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  reply	other threads:[~2021-06-04 17:51 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-25 18:32 [PATCH v3 00/20] arm64: entry: migrate more code to C Mark Rutland
2021-05-25 18:32 ` [PATCH v3 01/20] arm64: remove redundant local_daif_mask() in bad_mode() Mark Rutland
2021-05-27 12:34   ` Marc Zyngier
2021-05-25 18:32 ` [PATCH v3 02/20] arm64: entry: unmask IRQ+FIQ after EL0 handling Mark Rutland
2021-06-04 16:47   ` Will Deacon
2021-05-25 18:32 ` [PATCH v3 03/20] arm64: entry: convert SError handlers to C Mark Rutland
2021-05-25 18:32 ` [PATCH v3 04/20] arm64: entry: move arm64_preempt_schedule_irq to entry-common.c Mark Rutland
2021-05-25 18:32 ` [PATCH v3 05/20] arm64: entry: move preempt logic to C Mark Rutland
2021-06-04 15:43   ` Will Deacon
2021-06-04 16:54     ` Mark Rutland
2021-05-25 18:32 ` [PATCH v3 06/20] arm64: entry: add a call_on_irq_stack helper Mark Rutland
2021-05-25 18:32 ` [PATCH v3 07/20] arm64: entry: convert IRQ+FIQ handlers to C Mark Rutland
2021-05-25 18:32 ` [PATCH v3 08/20] arm64: entry: organise entry handlers consistently Mark Rutland
2021-06-04 16:51   ` Will Deacon
2021-06-04 17:39     ` Mark Rutland
2021-06-04 17:44       ` Will Deacon
2021-06-04 18:01         ` Mark Rutland
2021-05-25 18:32 ` [PATCH v3 09/20] arm64: entry: organise entry vectors consistently Mark Rutland
2021-05-25 18:32 ` [PATCH v3 10/20] arm64: entry: consolidate EL1 exception returns Mark Rutland
2021-05-25 18:32 ` [PATCH v3 11/20] arm64: entry: move bad_mode() to entry-common.c Mark Rutland
2021-06-04 16:57   ` Will Deacon
2021-06-04 17:42     ` Mark Rutland
2021-06-04 17:43       ` Will Deacon
2021-05-25 18:32 ` [PATCH v3 12/20] arm64: entry: improve bad_mode() Mark Rutland
2021-05-25 18:32 ` [PATCH v3 13/20] arm64: entry: template the entry asm functions Mark Rutland
2021-05-25 18:32 ` [PATCH v3 14/20] arm64: entry: handle all vectors with C Mark Rutland
2021-06-04 17:13   ` Will Deacon
2021-05-25 18:32 ` [PATCH v3 15/20] arm64: entry: fold el1_inv() into el1h_64_sync_handler() Mark Rutland
2021-05-25 18:32 ` [PATCH v3 16/20] arm64: entry: split bad stack entry Mark Rutland
2021-05-25 18:32 ` [PATCH v3 17/20] arm64: entry: split SDEI entry Mark Rutland
2021-05-25 18:33 ` [PATCH v3 18/20] arm64: entry: make NMI entry/exit functions static Mark Rutland
2021-05-25 18:33 ` [PATCH v3 19/20] arm64: entry: don't instrument entry code with KCOV Mark Rutland
2021-06-04 17:16   ` Will Deacon
2021-06-04 17:49     ` Mark Rutland [this message]
2021-05-25 18:33 ` [PATCH v3 20/20] arm64: idle: don't instrument idle " Mark Rutland
2021-05-27 14:06 ` [PATCH v3 00/20] arm64: entry: migrate more code to C Catalin Marinas
2021-05-27 15:31 ` Marc Zyngier

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