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Message-ID: <87o9h5sw4e.fsf@concordia.ellerman.id.au>
Date: Thu, 24 May 2018 11:03:29 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Boqun Feng <boqun.feng@...il.com>
Cc: Will Deacon <will.deacon@....com>,
Peter Zijlstra <peterz@...radead.org>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Andy Lutomirski <luto@...capital.net>,
Dave Watson <davejwatson@...com>,
linux-kernel <linux-kernel@...r.kernel.org>,
linux-api <linux-api@...r.kernel.org>,
Paul Turner <pjt@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Russell King <linux@....linux.org.uk>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, Andrew Hunter <ahh@...gle.com>,
Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
Ben Maurer <bmaurer@...com>, rostedt <rostedt@...dmis.org>,
Josh Triplett <josh@...htriplett.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Catalin Marinas <catalin.marinas@....com>,
Michael Kerrisk <mtk.manpages@...il.com>,
Joel Fernandes <joelaf@...gle.com>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 07/14] powerpc: Add support for restartable sequences
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> writes:
> ----- On May 23, 2018, at 4:14 PM, Mathieu Desnoyers mathieu.desnoyers@...icios.com wrote:
...
>>
>> Hi Boqun,
>>
>> I tried your patch in a ppc64 le environment, and it does not survive boot
>> with CONFIG_DEBUG_RSEQ=y. init gets killed right away.
Sorry this code is super gross and hard to deal with.
> The following fixup gets ppc64 to work:
>
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -208,6 +208,7 @@ system_call_exit:
> /* Check whether the syscall is issued inside a restartable sequence */
> addi r3,r1,STACK_FRAME_OVERHEAD
> bl rseq_syscall
> + ld r3,RESULT(r1)
> #endif
> /*
> * Disable interrupts so current_thread_info()->flags can't change,
I don't think that's safe.
If you look above that, we have r3, r8 and r12 all live:
.Lsyscall_exit:
std r3,RESULT(r1)
CURRENT_THREAD_INFO(r12, r1)
ld r8,_MSR(r1)
#ifdef CONFIG_PPC_BOOK3S
/* No MSR:RI on BookE */
andi. r10,r8,MSR_RI
beq- .Lunrecov_restore
#endif
They're all volatile across function calls:
http://openpowerfoundation.org/wp-content/uploads/resources/leabi/content/dbdoclet.50655240_68174.html
The system_call_exit symbol is actually there for kprobes and cosmetic
purposes. The actual syscall return flow starts at .Lsyscall_exit.
So I think this would work:
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index db4df061c33a..e19f377a25e0 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -184,6 +184,14 @@ system_call: /* label this so stack traces look sane */
.Lsyscall_exit:
std r3,RESULT(r1)
+
+#ifdef CONFIG_DEBUG_RSEQ
+ /* Check whether the syscall is issued inside a restartable sequence */
+ addi r3,r1,STACK_FRAME_OVERHEAD
+ bl rseq_syscall
+ ld r3,RESULT(r1)
+#endif
+
CURRENT_THREAD_INFO(r12, r1)
ld r8,_MSR(r1)
I'll try and get this series into my test setup at some point, been a
bit busy lately :)
cheers
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