linux-kernel - Re: [PATCH for 5.2 07/12] rseq/selftests: s390: use trap4 for RSEQ

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Date:   Thu, 16 May 2019 14:39:28 -0600
From:   shuah <shuah@...nel.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
        Ben Maurer <bmaurer@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH for 5.2 07/12] rseq/selftests: s390: use trap4 for
 RSEQ_SIG

Hi Mathieu,

On 4/29/19 9:27 AM, Mathieu Desnoyers wrote:
> From: Martin Schwidefsky <schwidefsky@...ibm.com>
> 
> Use trap4 as the guard instruction for the restartable sequence abort
> handler.
> 
> Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> ---
>   tools/testing/selftests/rseq/rseq-s390.h | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/rseq/rseq-s390.h b/tools/testing/selftests/rseq/rseq-s390.h
> index 7c4f3a70b6c7..1d05c5187ae6 100644
> --- a/tools/testing/selftests/rseq/rseq-s390.h
> +++ b/tools/testing/selftests/rseq/rseq-s390.h
> @@ -1,6 +1,13 @@
>   /* SPDX-License-Identifier: LGPL-2.1 OR MIT */
>   
> -#define RSEQ_SIG	0x53053053
> +/*
> + * RSEQ_SIG uses the trap4 instruction. As Linux does not make use of the
> + * access-register mode nor the linkage stack this instruction will always
> + * cause a special-operation exception (the trap-enabled bit in the DUCT
> + * is and will stay 0). The instruction pattern is
> + *	b2 ff 0f ff	trap4   4095(%r0)
> + */
> +#define RSEQ_SIG	0xB2FF0FFF
>   
>   #define rseq_smp_mb()	__asm__ __volatile__ ("bcr 15,0" ::: "memory")
>   #define rseq_smp_rmb()	rseq_smp_mb()
> 

I generated my pull request for Linus and did a sanity check and ran
into merge conflict on this patch. Looks like this is already in
Linus's tree.

Can you confirm!

I have to drop this patch and regenerate my pull request. Can you
confirm!

thanks,
-- Shuah