x86/cpu: Fix AMD erratum #1485 on Zen4-based CPUs

Fix erratum #1485 on Zen4 parts where running with STIBP disabled can
cause an #UD exception. The performance impact of the fix is negligible.
Reported-by: René Rebe <rene@exactcode.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: René Rebe <rene@exactcode.de>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/D99589F4-BC5D-430B-87B2-72C20370CF57@exactcode.com

arch/x86/include/asm/msr-index.h

@@ -637,12 +637,17 @@
 /* AMD Last Branch Record MSRs */
 #define MSR_AMD64_LBR_SELECT			0xc000010e
 
-/* Fam 17h MSRs */
-#define MSR_F17H_IRPERF			0xc00000e9
+/* Zen4 */
+#define MSR_ZEN4_BP_CFG			0xc001102e
+#define MSR_ZEN4_BP_CFG_SHARED_BTB_FIX_BIT 5
 
+/* Zen 2 */
 #define MSR_ZEN2_SPECTRAL_CHICKEN	0xc00110e3
 #define MSR_ZEN2_SPECTRAL_CHICKEN_BIT	BIT_ULL(1)
 
+/* Fam 17h MSRs */
+#define MSR_F17H_IRPERF			0xc00000e9
+
 /* Fam 16h MSRs */
 #define MSR_F16H_L2I_PERF_CTL		0xc0010230
 #define MSR_F16H_L2I_PERF_CTR		0xc0010231

arch/x86/kernel/cpu/amd.c

@@ -80,6 +80,10 @@ static const int amd_div0[] =
 	AMD_LEGACY_ERRATUM(AMD_MODEL_RANGE(0x17, 0x00, 0x0, 0x2f, 0xf),
 			   AMD_MODEL_RANGE(0x17, 0x50, 0x0, 0x5f, 0xf));
 
+static const int amd_erratum_1485[] =
+	AMD_LEGACY_ERRATUM(AMD_MODEL_RANGE(0x19, 0x10, 0x0, 0x1f, 0xf),
+			   AMD_MODEL_RANGE(0x19, 0x60, 0x0, 0xaf, 0xf));
+
 static bool cpu_has_amd_erratum(struct cpuinfo_x86 *cpu, const int *erratum)
 {
 	int osvw_id = *erratum++;
@@ -1149,6 +1153,10 @@ static void init_amd(struct cpuinfo_x86 *c)
 		pr_notice_once("AMD Zen1 DIV0 bug detected. Disable SMT for full protection.\n");
 		setup_force_cpu_bug(X86_BUG_DIV0);
 	}
+
+	if (!cpu_has(c, X86_FEATURE_HYPERVISOR) &&
+	     cpu_has_amd_erratum(c, amd_erratum_1485))
+		msr_set_bit(MSR_ZEN4_BP_CFG, MSR_ZEN4_BP_CFG_SHARED_BTB_FIX_BIT);
 }
 
 #ifdef CONFIG_X86_32