[SRU][J][PATCH v2 1/1] x86/CPU/AMD: Improve the erratum 1386 workaround

[Bethany Jamison]

From: "Borislav Petkov (AMD)" <bp at alien8.de>

BugLink: https://bugs.launchpad.net/bugs/2077321

Disable XSAVES only on machines which haven't loaded the microcode
revision containing the erratum fix.

This will come in handy when running archaic OSes as guests. OSes whose
brilliant programmers thought that CPUID is overrated and one should not
query it but use features directly, ala shoot first, ask questions
later... but only if you're alive after the shooting.

Signed-off-by: Borislav Petkov (AMD) <bp at alien8.de>
Tested-by: "Maciej S. Szmigiero" <maciej.szmigiero at oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky at oracle.com>
Link: https://lore.kernel.org/r/20240324200525.GBZgCHhYFsBj12PrKv@fat_crate.local
(backported from commit 29ba89f1895285f06c333546882e0c5ae9a6df23)
[bjamison: context conflict from neighboring line, Jammy is missing
'fix_erratum_1386' definition]
Signed-off-by: Bethany Jamison <bethany.jamison at canonical.com>
---
 arch/x86/include/asm/cpu_device_id.h |  8 ++++++++
 arch/x86/kernel/cpu/amd.c            | 12 ++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/arch/x86/include/asm/cpu_device_id.h b/arch/x86/include/asm/cpu_device_id.h
index e8e3dbe7f1730..b6325ee308718 100644
--- a/arch/x86/include/asm/cpu_device_id.h
+++ b/arch/x86/include/asm/cpu_device_id.h
@@ -288,6 +288,14 @@ struct x86_cpu_desc {
 	.x86_microcode_rev	= (revision),			\
 }
 
+#define AMD_CPU_DESC(fam, model, stepping, revision) {		\
+	.x86_family		= (fam),			\
+	.x86_vendor		= X86_VENDOR_AMD,		\
+	.x86_model		= (model),			\
+	.x86_stepping		= (stepping),			\
+	.x86_microcode_rev	= (revision),			\
+}
+
 extern const struct x86_cpu_id *x86_match_cpu(const struct x86_cpu_id *match);
 extern bool x86_cpu_has_min_microcode_rev(const struct x86_cpu_desc *table);
 
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index c99a16417cf03..cb8bd6145d1bc 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -13,6 +13,7 @@
 #include <asm/apic.h>
 #include <asm/cacheinfo.h>
 #include <asm/cpu.h>
+#include <asm/cpu_device_id.h>
 #include <asm/spec-ctrl.h>
 #include <asm/smp.h>
 #include <asm/numa.h>
@@ -931,6 +932,11 @@ static void init_amd_bd(struct cpuinfo_x86 *c)
 	clear_rdrand_cpuid_bit(c);
 }
 
+static const struct x86_cpu_desc erratum_1386_microcode[] = {
+	AMD_CPU_DESC(0x17,  0x1, 0x2, 0x0800126e),
+	AMD_CPU_DESC(0x17, 0x31, 0x0, 0x08301052),
+};
+
 void init_spectral_chicken(struct cpuinfo_x86 *c)
 {
 #ifdef CONFIG_CPU_UNRET_ENTRY
@@ -958,7 +964,13 @@ void init_spectral_chicken(struct cpuinfo_x86 *c)
 	 *
 	 * Affected parts all have no supervisor XSAVE states, meaning that
 	 * the XSAVEC instruction (which works fine) is equivalent.
+	 *
+	 * Clear the feature flag only on microcode revisions which
+	 * don't have the fix.
 	 */
+	if (x86_cpu_has_min_microcode_rev(erratum_1386_microcode))
+		return;
+
 	clear_cpu_cap(c, X86_FEATURE_XSAVES);
 }
 
-- 
2.34.1