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Message-ID: <174618201374.22196.15610752935421268143.tip-bot2@tip-bot2>
Date: Fri, 02 May 2025 10:33:33 -0000
From: "tip-bot2 for David Kaplan" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: David Kaplan <david.kaplan@....com>,
"Borislav Petkov (AMD)" <bp@...en8.de>, Josh Poimboeuf <jpoimboe@...nel.org>,
x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/bugs] x86/bugs: Restructure MDS mitigation
The following commit has been merged into the x86/bugs branch of tip:
Commit-ID: 559c758bc722ca0630d2b7f433f490cb76fe6128
Gitweb: https://git.kernel.org/tip/559c758bc722ca0630d2b7f433f490cb76fe6128
Author: David Kaplan <david.kaplan@....com>
AuthorDate: Fri, 18 Apr 2025 11:17:06 -05:00
Committer: Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Mon, 28 Apr 2025 12:53:33 +02:00
x86/bugs: Restructure MDS mitigation
Restructure MDS mitigation selection to use select/update/apply
functions to create consistent vulnerability handling.
[ bp: rename and beef up comment over VERW mitigation selected var for
maximum clarity. ]
Signed-off-by: David Kaplan <david.kaplan@....com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@...nel.org>
Link: https://lore.kernel.org/20250418161721.1855190-2-david.kaplan@amd.com
---
arch/x86/kernel/cpu/bugs.c | 61 +++++++++++++++++++++++++++++++++++--
1 file changed, 59 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 9131e61..f697e6b 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -34,6 +34,25 @@
#include "cpu.h"
+/*
+ * Speculation Vulnerability Handling
+ *
+ * Each vulnerability is handled with the following functions:
+ * <vuln>_select_mitigation() -- Selects a mitigation to use. This should
+ * take into account all relevant command line
+ * options.
+ * <vuln>_update_mitigation() -- This is called after all vulnerabilities have
+ * selected a mitigation, in case the selection
+ * may want to change based on other choices
+ * made. This function is optional.
+ * <vuln>_apply_mitigation() -- Enable the selected mitigation.
+ *
+ * The compile-time mitigation in all cases should be AUTO. An explicit
+ * command-line option can override AUTO. If no such option is
+ * provided, <vuln>_select_mitigation() will override AUTO to the best
+ * mitigation option.
+ */
+
static void __init spectre_v1_select_mitigation(void);
static void __init spectre_v2_select_mitigation(void);
static void __init retbleed_select_mitigation(void);
@@ -41,6 +60,8 @@ static void __init spectre_v2_user_select_mitigation(void);
static void __init ssb_select_mitigation(void);
static void __init l1tf_select_mitigation(void);
static void __init mds_select_mitigation(void);
+static void __init mds_update_mitigation(void);
+static void __init mds_apply_mitigation(void);
static void __init md_clear_update_mitigation(void);
static void __init md_clear_select_mitigation(void);
static void __init taa_select_mitigation(void);
@@ -172,6 +193,7 @@ void __init cpu_select_mitigations(void)
spectre_v2_user_select_mitigation();
ssb_select_mitigation();
l1tf_select_mitigation();
+ mds_select_mitigation();
md_clear_select_mitigation();
srbds_select_mitigation();
l1d_flush_select_mitigation();
@@ -182,6 +204,14 @@ void __init cpu_select_mitigations(void)
*/
srso_select_mitigation();
gds_select_mitigation();
+
+ /*
+ * After mitigations are selected, some may need to update their
+ * choices.
+ */
+ mds_update_mitigation();
+
+ mds_apply_mitigation();
}
/*
@@ -284,6 +314,12 @@ enum rfds_mitigations {
static enum rfds_mitigations rfds_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_RFDS) ? RFDS_MITIGATION_AUTO : RFDS_MITIGATION_OFF;
+/*
+ * Set if any of MDS/TAA/MMIO/RFDS are going to enable VERW clearing
+ * through X86_FEATURE_CLEAR_CPU_BUF on kernel and guest entry.
+ */
+static bool verw_clear_cpu_buf_mitigation_selected __ro_after_init;
+
static void __init mds_select_mitigation(void)
{
if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off()) {
@@ -294,12 +330,34 @@ static void __init mds_select_mitigation(void)
if (mds_mitigation == MDS_MITIGATION_AUTO)
mds_mitigation = MDS_MITIGATION_FULL;
+ if (mds_mitigation == MDS_MITIGATION_OFF)
+ return;
+
+ verw_clear_cpu_buf_mitigation_selected = true;
+}
+
+static void __init mds_update_mitigation(void)
+{
+ if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off())
+ return;
+
+ /* If TAA, MMIO, or RFDS are being mitigated, MDS gets mitigated too. */
+ if (verw_clear_cpu_buf_mitigation_selected)
+ mds_mitigation = MDS_MITIGATION_FULL;
+
if (mds_mitigation == MDS_MITIGATION_FULL) {
if (!boot_cpu_has(X86_FEATURE_MD_CLEAR))
mds_mitigation = MDS_MITIGATION_VMWERV;
+ }
- setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
+ pr_info("%s\n", mds_strings[mds_mitigation]);
+}
+static void __init mds_apply_mitigation(void)
+{
+ if (mds_mitigation == MDS_MITIGATION_FULL ||
+ mds_mitigation == MDS_MITIGATION_VMWERV) {
+ setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
if (!boot_cpu_has(X86_BUG_MSBDS_ONLY) &&
(mds_nosmt || cpu_mitigations_auto_nosmt()))
cpu_smt_disable(false);
@@ -602,7 +660,6 @@ out:
static void __init md_clear_select_mitigation(void)
{
- mds_select_mitigation();
taa_select_mitigation();
mmio_select_mitigation();
rfds_select_mitigation();
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