public inbox for linux-kernel@vger.kernel.org
 help / color / mirror / Atom feed
From: Peter Zijlstra <peterz@infradead.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: dwmw2@infradead.org, pjt@google.com,
	linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
	gregkh@linux-foundation.org, tim.c.chen@linux.intel.com,
	dave.hansen@intel.com, tglx@linutronix.de, luto@amacapital.net,
	Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH] x86/retpoline: Also fill return buffer after idle
Date: Tue, 9 Jan 2018 10:37:56 +0100	[thread overview]
Message-ID: <20180109093756.GF6176@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180108235126.28736-1-andi@firstfloor.org>

On Mon, Jan 08, 2018 at 03:51:26PM -0800, Andi Kleen wrote:

> @@ -107,8 +109,15 @@ static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
>  		}
>  
>  		__monitor((void *)&current_thread_info()->flags, 0, 0);
> -		if (!need_resched())
> +		if (!need_resched()) {
>  			__mwait(eax, ecx);
> +			/*
> +			 * idle could have cleared the return buffer,
> +			 * so fill it to prevent uncontrolled
> +			 * speculation.
> +			 */
> +			fill_return_buffer();

wouldn't something like:

			if (static_cpu_has(X86_FEATURE_RETPOLINE))
				fill_return_buffer();

be much saner? Then we avoid the entire call when not needed and you
don't have to muck with the asm either.

Also, you forgot mwait_idle() in process.c

> +		}
>  	}
>  	current_clr_polling();
>  }
> -- 
> 2.14.3
> 

  parent reply	other threads:[~2018-01-09  9:39 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-08 23:51 [PATCH] x86/retpoline: Also fill return buffer after idle Andi Kleen
2018-01-09  0:00 ` David Woodhouse
2018-01-09  0:24   ` Andi Kleen
2018-01-09  0:28     ` David Woodhouse
2018-01-09  9:37 ` Peter Zijlstra [this message]
2018-01-09 13:58   ` David Woodhouse
2018-01-09 14:12     ` Peter Zijlstra

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180109093756.GF6176@hirez.programming.kicks-ass.net \
    --to=peterz@infradead.org \
    --cc=ak@linux.intel.com \
    --cc=andi@firstfloor.org \
    --cc=dave.hansen@intel.com \
    --cc=dwmw2@infradead.org \
    --cc=gregkh@linux-foundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luto@amacapital.net \
    --cc=pjt@google.com \
    --cc=tglx@linutronix.de \
    --cc=tim.c.chen@linux.intel.com \
    --cc=torvalds@linux-foundation.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox