linux-kernel - Re: [PATCH RFC 1/2] x86/entry_64: Add a separate unmitigated entry/exit path

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Message-ID: <0402bea4-bb0a-4d67-9ae2-f534a6076861@redhat.com>
Date: Fri, 20 Sep 2024 02:57:34 -0400
From: Waiman Long <longman@...hat.com>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 David Kaplan <David.Kaplan@....com>,
 Daniel Sneddon <daniel.sneddon@...ux.intel.com>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH RFC 1/2] x86/entry_64: Add a separate unmitigated
 entry/exit path

On 9/19/24 17:52, Pawan Gupta wrote:
> CPU mitigations are deployed system-wide, but usually not all of the
> userspace is malicious. Yet, they suffer from the performance impact
> of the mitigations. This all or nothing approach is due to lack of a
> way for kernel to know which userspace can be trusted and which cannot.
>
> For scenarios where an admin can decide which processes to trust, an
> interface to tell the kernel to possibly skip the mitigation would be
> useful.
>
> In preparation for kernel to be able to selectively apply mitigation
> per-process add a separate kernel entry/exit path that skips the
> mitigations.
>
> Originally-by: Josh Poimboeuf <jpoimboe@...nel.org>
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>

For the current patch, not all x86 CPU vulnerability mitigations can be 
disabled. Maybe we should list the subset of mitigations that can be 
disabled.

Cheers,
Longman