linux-kernel - Re: [PATCH v2 3/6] x86: clean up _TIF_SYSCALL_EMU handling using ptrace_syscall

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Message-ID: <20190318153321.GA23521@redhat.com>
Date:   Mon, 18 Mar 2019 16:33:22 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Richard Weinberger <richard@....at>, jdike@...toit.com,
        Steve Capper <Steve.Capper@....com>,
        Haibo Xu <haibo.xu@....com>, Bin Lu <bin.lu@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v2 3/6] x86: clean up _TIF_SYSCALL_EMU handling using
 ptrace_syscall_enter hook

On 03/18, Sudeep Holla wrote:
>
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -70,22 +70,16 @@ static long syscall_trace_enter(struct pt_regs *regs)
>  
>  	struct thread_info *ti = current_thread_info();
>  	unsigned long ret = 0;
> -	bool emulated = false;
>  	u32 work;
>  
>  	if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
>  		BUG_ON(regs != task_pt_regs(current));
>  
> -	work = READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
> -
> -	if (unlikely(work & _TIF_SYSCALL_EMU))
> -		emulated = true;
> -
> -	if ((emulated || (work & _TIF_SYSCALL_TRACE)) &&
> -	    tracehook_report_syscall_entry(regs))
> +	if (unlikely(ptrace_syscall_enter(regs)))
>  		return -1L;
>  
> -	if (emulated)
> +	work = READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
> +	if ((work & _TIF_SYSCALL_TRACE) && tracehook_report_syscall_entry(regs))
>  		return -1L;

Well, I won't really argue, but to be honest I think this change doesn't make
the code better... With this patch tracehook_report_syscall_entry() has 2 callers,
to me this just adds some confusion.

I agree that the usage of emulated/_TIF_SYSCALL_EMU looks a bit overcomplicated,
I'd suggest a simple cleanup below.

And it seems that _TIF_WORK_SYSCALL_ENTRY needs some cleanups too... We don't need
"& _TIF_WORK_SYSCALL_ENTRY" in syscall_trace_enter, and _TIF_WORK_SYSCALL_ENTRY
should not include _TIF_NOHZ?

Oleg.


--- x/arch/x86/entry/common.c
+++ x/arch/x86/entry/common.c
@@ -70,23 +70,18 @@ static long syscall_trace_enter(struct pt_regs *regs)
 
 	struct thread_info *ti = current_thread_info();
 	unsigned long ret = 0;
-	bool emulated = false;
 	u32 work;
 
 	if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
 		BUG_ON(regs != task_pt_regs(current));
 
-	work = READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
+	work = READ_ONCE(ti->flags);
 
-	if (unlikely(work & _TIF_SYSCALL_EMU))
-		emulated = true;
-
-	if ((emulated || (work & _TIF_SYSCALL_TRACE)) &&
-	    tracehook_report_syscall_entry(regs))
-		return -1L;
-
-	if (emulated)
-		return -1L;
+	if (work & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
+		ret = tracehook_report_syscall_entry(regs);
+		if (ret || (work & _TIF_SYSCALL_EMU))
+			return -1L;
+	}
 
 #ifdef CONFIG_SECCOMP
 	/*