All of lore.kernel.org
 help / color / mirror / Atom feed
From: Thomas Gleixner <tglx@linutronix.de>
To: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: linux-kernel@vger.kernel.org, mingo@redhat.com,
	konrad.wilk@oracle.com, x86@kernel.org, srinivas.eeda@oracle.com,
	bp@suse.de, tim.c.chen@linux.intel.com, peterz@infradead.org,
	hpa@zytor.com
Subject: Re: [PATCH] x86/speculation: Update TIF_SPEC_IB before ibpb barrier
Date: Mon, 28 Jan 2019 09:36:51 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.21.1901280934270.1622@nanos.tec.linutronix.de> (raw)
In-Reply-To: <0aa09e77-1454-9eaf-ef67-b00518e6f2d2@oracle.com>

On Mon, 28 Jan 2019, Zhenzhong Duan wrote:
> On 2019/1/26 2:03, Thomas Gleixner wrote:
> > Bah, nonsense. Brain was clearly still out for lunch and I confused IBPB
> > and STIBP for a moment. cond_ibpb() is the thing issues in switch_mm() and
> > that is not leaving a stale MSR around because we only write to it when we
> > need the barrier. The bit is not stale because the barrier is only issued
> > with the write. The bit has not to be cleared.
> > 
> > So the only 'issue' what happens is that switch_to() either issues a
> > barrier too much or misses one. That's really not a problem.
> 
> Ok, yes, the purpose of this patch is to avoid the one missed barrier.

And that missed barrier is not worth it to do extra work in switch_to/mm
simply because it's a one off event and there is no way to exploit that
reliably.

Thanks,

	tglx

  reply	other threads:[~2019-01-28  8:36 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-18 11:09 [PATCH] x86/speculation: Update TIF_SPEC_IB before ibpb barrier Zhenzhong Duan
2019-01-23 12:45 ` Thomas Gleixner
2019-01-25 15:39   ` Thomas Gleixner
2019-01-25 18:03     ` Thomas Gleixner
2019-01-28  8:28       ` Zhenzhong Duan
2019-01-28  8:36         ` Thomas Gleixner [this message]
2019-01-28  8:42           ` Zhenzhong Duan

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=alpine.DEB.2.21.1901280934270.1622@nanos.tec.linutronix.de \
    --to=tglx@linutronix.de \
    --cc=bp@suse.de \
    --cc=hpa@zytor.com \
    --cc=konrad.wilk@oracle.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=srinivas.eeda@oracle.com \
    --cc=tim.c.chen@linux.intel.com \
    --cc=x86@kernel.org \
    --cc=zhenzhong.duan@oracle.com \
    /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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.