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 16:49:00 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     shuah <shuah@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <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>,
        rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>,
        schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH for 5.2 07/12] rseq/selftests: s390: use trap4 for
 RSEQ_SIG

----- On May 16, 2019, at 4:39 PM, shuah shuah@...nel.org wrote:

> 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!

I confirm, it went through the s390 maintainer tree, here is the
upstream commit already in Linus' master:

commit e24e4712efad737ca09ff299276737331cd021d9
Author: Martin Schwidefsky <schwidefsky@...ibm.com>
Date:   Wed Apr 10 12:28:41 2019 +0200

    s390/rseq: use trap4 for RSEQ_SIG
    
    Use trap4 as the guard instruction for the restartable sequence abort
    handler.
    
    Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>

So you can either drop it from your end of the pull request, or Linus will
deal with the merge, as you prefer.

Thanks!

Mathieu


> 
> thanks,
> -- Shuah

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com