[tip: x86/bugs] x86/bugs: Restructure GDS mitigation

tip-bot2 for David Kaplan
2025-05-02T10:33:31Z

The following commit has been merged into the x86/bugs branch of tip:

Commit-ID: 9dcad2fb31bd9b9b860c515859625a065dd6e656
Gitweb: https://git.kernel.org/tip/9dcad2fb31bd9b9b860c515859625a065dd6e656
Author: David Kaplan <david.kaplan@amd.com>
AuthorDate: Fri, 18 Apr 2025 11:17:12 -05:00
Committer: Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Mon, 28 Apr 2025 15:19:30 +02:00

x86/bugs: Restructure GDS mitigation

Restructure GDS mitigation to use select/apply functions to create
consistent vulnerability handling.

Define new AUTO mitigation for GDS.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/20250418161721.1855190-8-david.kaplan@amd.com
---
arch/x86/kernel/cpu/bugs.c | 43 ++++++++++++++++++++++++-------------
1 file changed, 29 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 25b74a7..b070ad7 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -76,6 +76,7 @@ static void __init srbds_apply_mitigation(void);
static void __init l1d_flush_select_mitigation(void);
static void __init srso_select_mitigation(void);
static void __init gds_select_mitigation(void);
+static void __init gds_apply_mitigation(void);

/* The base value of the SPEC_CTRL MSR without task-specific bits set */
u64 x86_spec_ctrl_base;
@@ -227,6 +228,7 @@ void __init cpu_select_mitigations(void)
mmio_apply_mitigation();
rfds_apply_mitigation();
srbds_apply_mitigation();
+ gds_apply_mitigation();
}

/*
@@ -831,6 +833,7 @@ early_param("l1d_flush", l1d_flush_parse_cmdline);

enum gds_mitigations {
GDS_MITIGATION_OFF,
+ GDS_MITIGATION_AUTO,
GDS_MITIGATION_UCODE_NEEDED,
GDS_MITIGATION_FORCE,
GDS_MITIGATION_FULL,
@@ -839,7 +842,7 @@ enum gds_mitigations {
};

static enum gds_mitigations gds_mitigation __ro_after_init =
- IS_ENABLED(CONFIG_MITIGATION_GDS) ? GDS_MITIGATION_FULL : GDS_MITIGATION_OFF;
+ IS_ENABLED(CONFIG_MITIGATION_GDS) ? GDS_MITIGATION_AUTO : GDS_MITIGATION_OFF;

static const char * const gds_strings[] = {
[GDS_MITIGATION_OFF] = "Vulnerable",
@@ -880,6 +883,7 @@ void update_gds_msr(void)
case GDS_MITIGATION_FORCE:
case GDS_MITIGATION_UCODE_NEEDED:
case GDS_MITIGATION_HYPERVISOR:
+ case GDS_MITIGATION_AUTO:
return;
}

@@ -903,26 +907,21 @@ static void __init gds_select_mitigation(void)

if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
gds_mitigation = GDS_MITIGATION_HYPERVISOR;
- goto out;
+ return;
}

if (cpu_mitigations_off())
gds_mitigation = GDS_MITIGATION_OFF;
/* Will verify below that mitigation _can_ be disabled */

+ if (gds_mitigation == GDS_MITIGATION_AUTO)
+ gds_mitigation = GDS_MITIGATION_FULL;
+
/* No microcode */
if (!(x86_arch_cap_msr & ARCH_CAP_GDS_CTRL)) {
- if (gds_mitigation == GDS_MITIGATION_FORCE) {
- /*
- * This only needs to be done on the boot CPU so do it
- * here rather than in update_gds_msr()
- */
- setup_clear_cpu_cap(X86_FEATURE_AVX);
- pr_warn("Microcode update needed! Disabling AVX as mitigation.\n");
- } else {
+ if (gds_mitigation != GDS_MITIGATION_FORCE)
gds_mitigation = GDS_MITIGATION_UCODE_NEEDED;
- }
- goto out;
+ return;
}

/* Microcode has mitigation, use it */
@@ -943,9 +942,25 @@ static void __init gds_select_mitigation(void)
*/
gds_mitigation = GDS_MITIGATION_FULL_LOCKED;
}
+}
+
+static void __init gds_apply_mitigation(void)
+{
+ if (!boot_cpu_has_bug(X86_BUG_GDS))
+ return;
+
+ /* Microcode is present */
+ if (x86_arch_cap_msr & ARCH_CAP_GDS_CTRL)
+ update_gds_msr();
+ else if (gds_mitigation == GDS_MITIGATION_FORCE) {
+ /*
+ * This only needs to be done on the boot CPU so do it
+ * here rather than in update_gds_msr()
+ */
+ setup_clear_cpu_cap(X86_FEATURE_AVX);
+ pr_warn("Microcode update needed! Disabling AVX as mitigation.\n");
+ }

- update_gds_msr();
-out:
pr_info("%s\n", gds_strings[gds_mitigation]);
}