linux-kernel - Re: [PATCH 2/2] x86/bugs: spectre user default must depend on MITIGATION_SPECTRE

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Message-ID: <20241030183920.s4lk33ckvqtkguzm@desk>
Date: Wed, 30 Oct 2024 11:40:53 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Breno Leitao <leitao@...ian.org>
Cc: bp@...en8.de, x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, kernel-team@...a.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86/bugs: spectre user default must depend on
 MITIGATION_SPECTRE_V2

On Tue, Oct 29, 2024 at 02:19:12AM -0700, Breno Leitao wrote:
> > If this is the intention it should be
> > clearly documented that enabling kernel mitigation does not enable user
> > mitigation. And an explicit spectre_v2_user= is required to enable user
> > mitigation.
> 
> That is fair. I didn't find a place where to document about diferent
> behavior when CONFIG_MITIGATION_X is disabled. What would you suggest?

You could describe the behavior in the commit message and update kernel
parameter documentation.

With that:

Reviewed-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>

---
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 1518343bbe22..f8bc02cd10ec 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6241,6 +6241,8 @@
 
 			Selecting 'on' will also enable the mitigation
 			against user space to user space task attacks.
+			Selecting specific mitigation does not force enable
+			user mitigations.
 
 			Selecting 'off' will disable both the kernel and
 			the user space protections.