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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: Fri, 25 Jan 2019 16:39:09 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.21.1901251637480.1622@nanos.tec.linutronix.de> (raw)
In-Reply-To: <alpine.DEB.2.21.1901231335570.1628@nanos.tec.linutronix.de>

On Wed, 23 Jan 2019, Thomas Gleixner wrote:

> On Fri, 18 Jan 2019, Zhenzhong Duan wrote:
> 
> > When a task is set for updating TIF_SPEC_IB throuth SECCOMP by others
> > and it's scheduled in the first time, a stale TIF_SPEC_IB value is
> > picked in cond_ibpb(). This is due to TIF_SPEC_IB is updated later at
> > __switch_to_xtra().
> > 
> > Add an extra call to speculation_ctrl_update_tif() to update it before
> > IBPB barrier.
> 
> Errm. No. It adds that call to speculation_ctrl_update_tif() for every
> mm switch, most of the time for nothing.
> 
> If at all, and we discussed that before and decided not to worry about it
> (because it gets fixed up on the next context switch), then you want to
> handle ibpb() from there:

Actually we need to do that. It's not only the scheduled in first
problem. That whole thing might become completely stale in either
direction. Care to whip up a patch?

Thanks,

	tglx

  reply	other threads:[~2019-01-25 15:39 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 [this message]
2019-01-25 18:03     ` Thomas Gleixner
2019-01-28  8:28       ` Zhenzhong Duan
2019-01-28  8:36         ` Thomas Gleixner
2019-01-28  8:42           ` Zhenzhong Duan

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