From: Catalin Marinas <catalin.marinas@arm.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@kernel.org>, Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Marc Zyngier <maz@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: [RFC patch 07/15] arm64/syscall: Remove obscure flag check
Date: Fri, 20 Sep 2019 15:29:20 +0100 [thread overview]
Message-ID: <20190920142920.GB21231@arrakis.emea.arm.com> (raw)
In-Reply-To: <20190919150809.145400160@linutronix.de>
On Thu, Sep 19, 2019 at 05:03:21PM +0200, Thomas Gleixner wrote:
> The syscall handling code has an obscure check of pending work which does a
> shortcut before returning to user space. It calls into the exit work code
> when the flags at entry time required an entry into the slowpath. That does
> not make sense because the underlying work functionality will reevaluate
> the flags anyway and not do anything.
The current C code was just matching the original behaviour in asm
(converted by commit f37099b6992a0b81). The idea IIRC was to always pair
a syscall_trace_enter() with a syscall_trace_exit() irrespective of the
thread flag changes. I think the behaviour is preserved with your patch
if no-one clears the work flags during el0_svc_common().
> @@ -105,33 +103,15 @@ static void el0_svc_common(struct pt_reg
> user_exit();
>
> scno = syscall_enter_from_usermode(regs, scno);
> - if (scno == NO_SYSCALL)
> - goto trace_exit;
> -
> - invoke_syscall(regs, scno, sc_nr, syscall_table);
> + if (scno != NO_SYSCALL)
> + invoke_syscall(regs, scno, sc_nr, syscall_table);
>
> - /*
> - * The tracing status may have changed under our feet, so we have to
> - * check again. However, if we were tracing entry, then we always trace
> - * exit regardless, as the old entry assembly did.
> - */
> - if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
> - local_daif_mask();
> - flags = current_thread_info()->flags;
> - if (!has_syscall_work(flags)) {
> - /*
> - * We're off to userspace, where interrupts are
> - * always enabled after we restore the flags from
> - * the SPSR.
> - */
> - trace_hardirqs_on();
> - return;
> - }
> + local_daif_mask();
> + if (has_syscall_work(current_thread_info()->flags) ||
> + IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
> local_daif_restore(DAIF_PROCCTX);
> + syscall_trace_exit(regs);
> }
That's missing a trace_hardirqs_on() (off done in local_daif_mask())
before returning.
> -
> -trace_exit:
> - syscall_trace_exit(regs);
> }
--
Catalin
next prev parent reply other threads:[~2019-09-20 14:29 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-19 15:03 [RFC patch 00/15] entry: Provide generic implementation for host and guest entry/exit work Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 01/15] entry: Provide generic syscall entry functionality Thomas Gleixner
2019-09-20 23:38 ` Andy Lutomirski
2019-10-20 11:49 ` Thomas Gleixner
2019-09-23 9:05 ` Mike Rapoport
2019-09-19 15:03 ` [RFC patch 02/15] x86/entry: Remove _TIF_NOHZ from _TIF_WORK_SYSCALL_ENTRY Thomas Gleixner
2019-09-20 23:39 ` Andy Lutomirski
2019-09-23 20:43 ` Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 03/15] x86/entry: Use generic syscall entry function Thomas Gleixner
2019-09-20 23:41 ` Andy Lutomirski
2019-09-23 8:31 ` Peter Zijlstra
2019-09-23 8:40 ` Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 04/15] arm64/entry: " Thomas Gleixner
2019-09-20 12:21 ` Catalin Marinas
2019-09-19 15:03 ` [RFC patch 05/15] entry: Provide generic syscall exit function Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 06/15] x86/entry: Use generic syscall exit functionality Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 07/15] arm64/syscall: Remove obscure flag check Thomas Gleixner
2019-09-20 14:29 ` Catalin Marinas [this message]
2019-09-19 15:03 ` [RFC patch 08/15] arm64/syscall: Use generic syscall exit functionality Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 09/15] entry: Provide generic exit to usermode functionality Thomas Gleixner
2019-09-23 8:30 ` Peter Zijlstra
2019-09-19 15:03 ` [RFC patch 10/15] x86/entry: Move irq tracing to C code Thomas Gleixner
2019-09-23 8:47 ` Peter Zijlstra
2019-09-23 10:27 ` Thomas Gleixner
2019-09-23 11:49 ` Peter Zijlstra
2019-09-23 11:55 ` Peter Zijlstra
2019-09-23 12:10 ` Peter Zijlstra
2019-09-23 17:24 ` Andy Lutomirski
2019-09-26 2:59 ` Josh Poimboeuf
2019-09-19 15:03 ` [RFC patch 11/15] x86/entry: Use generic exit to usermode Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 12/15] arm64/entry: " Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 13/15] arm64/entry: Move FPU restore out of exit_to_usermode() loop Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 14/15] workpending: Provide infrastructure for work before entering a guest Thomas Gleixner
2019-09-19 15:40 ` Paolo Bonzini
2019-09-20 11:48 ` Thomas Gleixner
2019-09-23 18:17 ` Andy Lutomirski
2019-09-26 11:35 ` Miroslav Benes
2019-09-19 15:03 ` [RFC patch 15/15] x86/kvm: Use GENERIC_EXIT_WORKPENDING Thomas Gleixner
2019-09-19 15:40 ` Paolo Bonzini
2019-09-20 15:12 ` [RFC patch 00/15] entry: Provide generic implementation for host and guest entry/exit work Mark Rutland
2019-09-23 20:50 ` Thomas Gleixner
2019-09-23 18:18 ` Andy Lutomirski
2019-09-24 6:50 ` Christian Borntraeger
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