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From: Thomas Gleixner <tglx@linutronix.de>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Sebastian Lackner <sebastian@fds-team.de>,
	X86 ML <x86@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Anish Bhatt <anish@chelsio.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Chuck Ebbert <cebbert.lkml@gmail.com>,
	stable@kernel.org
Subject: Re: [PATCH 1/2] x86_64,entry: Filter RFLAGS.NT on entry from userspace
Date: Wed, 1 Oct 2014 00:27:41 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.11.1410010025050.4455@nanos> (raw)
In-Reply-To: <CALCETrX86zeONHsf74yKseddXUc1BMHHAFaGKgU82HuU9+_PjQ@mail.gmail.com>

On Tue, 30 Sep 2014, Andy Lutomirski wrote:
> It would certainly be possible to clear NT and retry IRET if IRET
> fails with NT set.  This would have no overhead for anything relevant.
> That would be this alternative from my 0/2 email:
> 
>  - Don't filter NT on sysenter.  Instead, filter it on EFI entry
>    and modify the IRET code to retry without NT set if NT was set.
> 
> Thomas hpa, etc: any thoughts?

Filter it right away. That's solid and obvious. Anything else is just
complex and prone for future brown paperbag failures.

We get the context switch benefit from it, so there is some
compensation for the extra cycles.

Thanks,

	tglx

  parent reply	other threads:[~2014-09-30 22:27 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-30 19:40 [PATCH 0/2] x86_64,entry: Clear NT on entry and speed up switch_to Andy Lutomirski
2014-09-30 19:40 ` [PATCH 1/2] x86_64,entry: Filter RFLAGS.NT on entry from userspace Andy Lutomirski
2014-09-30 21:39   ` Sebastian Lackner
2014-09-30 21:45     ` Andy Lutomirski
2014-09-30 22:23       ` Sebastian Lackner
2014-09-30 22:27       ` Thomas Gleixner [this message]
2014-09-30 22:33         ` Andy Lutomirski
2014-09-30 23:21           ` Thomas Gleixner
2014-10-01 17:50             ` H. Peter Anvin
2014-10-01 17:53               ` H. Peter Anvin
2014-09-30 22:42         ` H. Peter Anvin
2014-10-01  0:27   ` Chuck Ebbert
2014-10-01  0:38     ` Andy Lutomirski
2014-09-30 19:40 ` [PATCH 2/2] x86_64: Don't save flags on context switch Andy Lutomirski
2014-09-30 22:21 ` [PATCH 0/2] x86_64,entry: Clear NT on entry and speed up switch_to Thomas Gleixner
2014-09-30 22:30   ` Andy Lutomirski

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