From: Andi Kleen <ak@linux.intel.com>
To: Waiman Long <longman@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
Jonathan Corbet <corbet@lwn.net>,
x86@kernel.org, linux-kernel@vger.kernel.org,
linux-doc@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
David Woodhouse <dwmw@amazon.co.uk>,
Jiri Kosina <jikos@kernel.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
KarimAllah Ahmed <karahmed@amazon.de>,
Peter Zijlstra <peterz@infradead.org>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [RFC PATCH] x86/speculation: Don't inherit TIF_SSBD on execve()
Date: Wed, 19 Dec 2018 11:38:22 -0800 [thread overview]
Message-ID: <20181219193822.GU25620@tassilo.jf.intel.com> (raw)
In-Reply-To: <1545246590-12704-1-git-send-email-longman@redhat.com>
On Wed, Dec 19, 2018 at 02:09:50PM -0500, Waiman Long wrote:
> With the default SPEC_STORE_BYPASS_SECCOMP/SPEC_STORE_BYPASS_PRCTL mode,
> the TIF_SSBD bit will be inherited when a new task is fork'ed or cloned.
>
> As only certain class of applications (like Java) requires disabling
> speculative store bypass for security purpose, it may not make sense to
> allow the TIF_SSBD bit to be inherited across execve() boundary where the
> new application may not need SSBD at all and is probably not aware that
> SSBD may have been turned on. This may cause an unnecessary performance
> loss of up to 20% in some cases.
>
> The arch_setup_new_exec() function is updated to clear the TIF_SSBD
> bit unless it has been force-disabled.
This makes it impossible to write a wrapper that turns this mode
on for unmodified programs.
Do you have a real use case where this behavior is a problem?
-Andi
next prev parent reply other threads:[~2018-12-19 19:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-19 19:09 [RFC PATCH] x86/speculation: Don't inherit TIF_SSBD on execve() Waiman Long
2018-12-19 19:38 ` Andi Kleen [this message]
2018-12-19 19:45 ` Waiman Long
2018-12-20 0:58 ` Andi Kleen
2019-01-07 14:49 ` Waiman Long
2019-01-11 19:52 ` Thomas Gleixner
2019-01-14 21:46 ` Waiman Long
2019-01-15 9:48 ` Thomas Gleixner
2019-01-15 15:54 ` Waiman Long
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