linux-kernel - Re: [PATCH v4] x86/bugs: Add a separate config for each mitigation

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Message-ID: <20231011164955.mm5ipmuyf4rje5u3@treble>
Date:   Wed, 11 Oct 2023 09:49:55 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Breno Leitao <leitao@...ian.org>
Cc:     tglx@...utronix.de, bp@...en8.de, Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, leit@...a.com,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] x86/bugs: Add a separate config for each mitigation

On Wed, Oct 11, 2023 at 05:20:59AM -0700, Breno Leitao wrote:
> On Tue, Oct 10, 2023 at 09:42:52PM -0700, Josh Poimboeuf wrote:
> > On Tue, Oct 10, 2023 at 03:30:27AM -0700, Breno Leitao wrote:
> > > +config MITIGATE_MDS
> > > +	bool "Mitigate Microarchitectural Data Sampling (MDS) hardware bug"
> > > +	depends on CPU_SUP_INTEL
> > > +	default y
> > > +	help
> > > +	  Enable mitigation for Microarchitectural Data Sampling (MDS). MDS is
> > > +	  a hardware vulnerability which allows unprivileged speculative access
> > > +	  to data which is available in various CPU internal buffer. Deeper
> > > +	  technical information is available in the MDS specific x86 architecture
> > > +	  section: Documentation/arch/x86/mds.rst.
> > 
> > MITIGATE_GDS seems to be missing?
> 
> GDS is named `GDS_FORCE_MITIGATION` instead of  MITIGATE_GDS. See
> 11cf22869ea ("x86/speculation: Add Kconfig option for GDS")

Enabling/disabling GDS_FORCE_MITIGATION doesn't enable/disable the
mitigation, it just changes the default.

For consistency that option should probably be renamed to
MITIGATION_GDS_FORCE.  It should depend on MITIGATION_GDS.  If
MITIGATION_GDS is disabled, gds_mitigation should default to
GDS_MITIGATION_OFF.

e.g., something like

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 66bfabae8814..c8c879302b37 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2549,9 +2549,16 @@ config SLS
 	  against straight line speculation. The kernel image might be slightly
 	  larger.
 
-config GDS_FORCE_MITIGATION
-	bool "Force GDS Mitigation"
+config MITIGATION_GDS
+	bool" Mitigate Gather Data Sampling"
 	depends on CPU_SUP_INTEL
+	default y
+	help
+	  (Insert actual description here)
+
+config MITIGATION_GDS_FORCE
+	bool "Force GDS Mitigation"
+	depends on MITIGATION_GDS
 	default n
 	help
 	  Gather Data Sampling (GDS) is a hardware vulnerability which allows
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index f081d26616ac..43ad3eee3d4c 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -671,11 +671,15 @@ enum gds_mitigations {
 	GDS_MITIGATION_HYPERVISOR,
 };
 
-#if IS_ENABLED(CONFIG_GDS_FORCE_MITIGATION)
+#if IS_ENABLED(CONFIG_MITIGATION_GDS)
+#if IS_ENABLED(CONFIG_MITIGATION_GDS_FORCE)
 static enum gds_mitigations gds_mitigation __ro_after_init = GDS_MITIGATION_FORCE;
 #else
 static enum gds_mitigations gds_mitigation __ro_after_init = GDS_MITIGATION_FULL;
 #endif
+#else
+static enum gds_mitigations gds_mitigation __ro_after_init = GDS_MITIGATION_OFF;
+#endif
 
 static const char * const gds_strings[] = {
 	[GDS_MITIGATION_OFF]		= "Vulnerable",