From: "H. Peter Anvin" <hpa@zytor.com>
To: Andy Lutomirski <luto@amacapital.net>,
Thomas Gleixner <tglx@linutronix.de>, X86 ML <x86@kernel.org>,
Ingo Molnar <mingo@redhat.com>
Cc: Sebastian Lackner <sebastian@fds-team.de>,
Anish Bhatt <anish@chelsio.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Chuck Ebbert <cebbert.lkml@gmail.com>,
stable@vger.kernel.org
Subject: Re: [PATCH v2 1/2] x86_64,entry: Filter RFLAGS.NT on entry from userspace
Date: Wed, 01 Oct 2014 08:22:16 -0700 [thread overview]
Message-ID: <542C1C28.9050408@zytor.com> (raw)
In-Reply-To: <0e906bdeba3660c9766248d3d7229e78a423ca5b.1412138935.git.luto@amacapital.net>
On 09/30/2014 09:51 PM, Andy Lutomirski wrote:
>
> diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
> index 4299eb05023c..44d1dd371454 100644
> --- a/arch/x86/ia32/ia32entry.S
> +++ b/arch/x86/ia32/ia32entry.S
> @@ -151,6 +151,18 @@ ENTRY(ia32_sysenter_target)
> 1: movl (%rbp),%ebp
> _ASM_EXTABLE(1b,ia32_badarg)
> ASM_CLAC
> +
> + /*
> + * Sysenter doesn't filter flags, so we need to clear NT
> + * ourselves. To save a few cycles, we can check whether
> + * NT was set instead of doing an unconditional popfq.
> + */
> + testl $X86_EFLAGS_NT,EFLAGS(%rsp) /* saved EFLAGS match cpu */
> + jz 1f
> + pushq_cfi $(X86_EFLAGS_IF|X86_EFLAGS_FIXED)
> + popfq_cfi
> +1:
> +
I'm wondering if it would be easier to just remove ASM_CLAC and do this
unconditionally. On SMAP-enabled hardware then that gives us back some
of the cycles, may make the branch unnecessary.
-hpa
next prev parent reply other threads:[~2014-10-01 15:22 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-01 4:51 [PATCH v2 0/2] x86_64,entry: Clear NT on entry and speed up switch_to Andy Lutomirski
2014-10-01 4:51 ` [PATCH v2 1/2] x86_64,entry: Filter RFLAGS.NT on entry from userspace Andy Lutomirski
2014-10-01 5:09 ` Sebastian Lackner
2014-10-01 5:24 ` Andy Lutomirski
2014-10-01 15:19 ` H. Peter Anvin
2014-10-01 14:09 ` Chuck Ebbert
2014-10-01 14:32 ` Chuck Ebbert
2014-10-01 14:46 ` Andy Lutomirski
2014-10-01 14:56 ` Chuck Ebbert
2014-10-01 15:03 ` Andy Lutomirski
2014-10-01 15:22 ` H. Peter Anvin [this message]
2014-10-01 15:26 ` H. Peter Anvin
2014-10-01 15:50 ` Andy Lutomirski
2014-10-01 16:04 ` Andy Lutomirski
2014-10-01 16:17 ` H. Peter Anvin
2014-10-01 4:51 ` [PATCH v2 2/2] x86_64: Don't save flags on context switch Andy Lutomirski
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