From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [PATCH 07/14] powerpc: Add support for restartable sequences Date: Wed, 23 May 2018 17:29:45 -0400 (EDT) Message-ID: <37442352.1577.1527110985175.JavaMail.zimbra@efficios.com> References: <20180430224433.17407-1-mathieu.desnoyers@efficios.com> <112970629.1913.1526501596485.JavaMail.zimbra@efficios.com> <20180517011949.GA1121@tardis> <277374719.2144.1526570889798.JavaMail.zimbra@efficios.com> <1526601043.1338308.1376191416.0444B8C5@webmail.messagingengine.com> <418003803.516.1526667437396.JavaMail.zimbra@efficios.com> <20180520140811.GB1121@tardis> <1928158599.1541.1527106479862.JavaMail.zimbra@efficios.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1928158599.1541.1527106479862.JavaMail.zimbra@efficios.com> Sender: linux-kernel-owner@vger.kernel.org To: Boqun Feng Cc: Will Deacon , Peter Zijlstra , "Paul E. McKenney" , Andy Lutomirski , Dave Watson , linux-kernel , linux-api , Paul Turner , Andrew Morton , Russell King , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrew Hunter , Andi Kleen , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Linus Torvalds , Catalin Marinas List-Id: linux-api@vger.kernel.org ----- On May 23, 2018, at 4:14 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote: > ----- On May 20, 2018, at 10:08 AM, Boqun Feng boqun.feng@gmail.com wrote: > >> On Fri, May 18, 2018 at 02:17:17PM -0400, Mathieu Desnoyers wrote: >>> ----- On May 17, 2018, at 7:50 PM, Boqun Feng boqun.feng@gmail.com wrote: >>> [...] >>> >> > I think you're right. So we have to introduce callsite to rseq_syscall() >>> >> > in syscall path, something like: >>> >> > >>> >> > diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S >>> >> > index 51695608c68b..a25734a96640 100644 >>> >> > --- a/arch/powerpc/kernel/entry_64.S >>> >> > +++ b/arch/powerpc/kernel/entry_64.S >>> >> > @@ -222,6 +222,9 @@ system_call_exit: >>> >> > mtmsrd r11,1 >>> >> > #endif /* CONFIG_PPC_BOOK3E */ >>> >> > >>> >> > + addi r3,r1,STACK_FRAME_OVERHEAD >>> >> > + bl rseq_syscall >>> >> > + >>> >> > ld r9,TI_FLAGS(r12) >>> >> > li r11,-MAX_ERRNO >>> >> > andi. >>> >> > r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK) >>> >> > >>> >>> By the way, I think this is not the right spot to call rseq_syscall, because >>> interrupts are disabled. I think we should move this hunk right after >>> system_call_exit. >>> >> >> Good point. >> >>> Would you like to implement and test an updated patch adding those calls for ppc >>> 32 and 64 ? >>> >> >> I'd like to help, but I don't have a handy ppc environment for test... >> So I made the below patch which has only been build-tested, hope it >> could be somewhat helpful. > > 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. 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, > Moreover, I'm not sure that the r3 register don't contain something worth > saving before the call on ppc32. Just after there is a "mr" instruction > which AFAIU takes r3 as input register. I'll start testing on ppc32 now. Thanks, Mathieu > > Can you look into it ? > > Thanks, > > Mathieu > >> >> Regards, >> Boqun >> >> --------------------------------->8 >> Subject: [PATCH] powerpc: Add syscall detection for restartable sequences >> >> Syscalls are not allowed inside restartable sequences, so add a call to >> rseq_syscall() at the very beginning of system call exiting path for >> CONFIG_DEBUG_RSEQ=y kernel. This could help us to detect whether there >> is a syscall issued inside restartable sequences. >> >> Signed-off-by: Boqun Feng >> --- >> arch/powerpc/kernel/entry_32.S | 5 +++++ >> arch/powerpc/kernel/entry_64.S | 5 +++++ >> 2 files changed, 10 insertions(+) >> >> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S >> index eb8d01bae8c6..2f134eebe7ed 100644 >> --- a/arch/powerpc/kernel/entry_32.S >> +++ b/arch/powerpc/kernel/entry_32.S >> @@ -365,6 +365,11 @@ syscall_dotrace_cont: >> blrl /* Call handler */ >> .globl ret_from_syscall >> ret_from_syscall: >> +#ifdef CONFIG_DEBUG_RSEQ >> + /* Check whether the syscall is issued inside a restartable sequence */ >> + addi r3,r1,STACK_FRAME_OVERHEAD >> + bl rseq_syscall >> +#endif >> mr r6,r3 >> CURRENT_THREAD_INFO(r12, r1) >> /* disable interrupts so current_thread_info()->flags can't change */ >> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S >> index 2cb5109a7ea3..2e2d59bb45d0 100644 >> --- a/arch/powerpc/kernel/entry_64.S >> +++ b/arch/powerpc/kernel/entry_64.S >> @@ -204,6 +204,11 @@ system_call: /* label this so stack traces look sane */ >> * This is blacklisted from kprobes further below with _ASM_NOKPROBE_SYMBOL(). >> */ >> system_call_exit: >> +#ifdef CONFIG_DEBUG_RSEQ >> + /* Check whether the syscall is issued inside a restartable sequence */ >> + addi r3,r1,STACK_FRAME_OVERHEAD >> + bl rseq_syscall >> +#endif >> /* >> * Disable interrupts so current_thread_info()->flags can't change, >> * and so that we don't get interrupted after loading SRR0/1. >> -- >> 2.16.2 > > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com