x86/cpu/amd: Add Spectral Chicken

Zen2 uarchs have an undocumented, unnamed, MSR that contains a chicken
bit for some speculation behaviour. It needs setting.

Note: very belatedly AMD released naming; it's now officially called
      MSR_AMD64_DE_CFG2 and MSR_AMD64_DE_CFG2_SUPPRESS_NOBR_PRED_BIT
      but shall remain the SPECTRAL CHICKEN.

Suggested-by: Andrew Cooper <Andrew.Cooper3@citrix.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 059c7e5..7b411d9 100644 (file)
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -568,6 +568,9 @@
 /* Fam 17h MSRs */
 #define MSR_F17H_IRPERF                        0xc00000e9
 
+#define MSR_ZEN2_SPECTRAL_CHICKEN      0xc00110e3
+#define MSR_ZEN2_SPECTRAL_CHICKEN_BIT  BIT_ULL(1)
+
 /* Fam 16h MSRs */
 #define MSR_F16H_L2I_PERF_CTL          0xc0010230
 #define MSR_F16H_L2I_PERF_CTR          0xc0010231

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 0c0b097..8cf0659 100644 (file)
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -862,6 +862,26 @@ static void init_amd_bd(struct cpuinfo_x86 *c)
        clear_rdrand_cpuid_bit(c);
 }
 
+void init_spectral_chicken(struct cpuinfo_x86 *c)
+{
+       u64 value;
+
+       /*
+        * On Zen2 we offer this chicken (bit) on the altar of Speculation.
+        *
+        * This suppresses speculation from the middle of a basic block, i.e. it
+        * suppresses non-branch predictions.
+        *
+        * We use STIBP as a heuristic to filter out Zen2 from the rest of F17H
+        */
+       if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && cpu_has(c, X86_FEATURE_AMD_STIBP)) {
+               if (!rdmsrl_safe(MSR_ZEN2_SPECTRAL_CHICKEN, &value)) {
+                       value |= MSR_ZEN2_SPECTRAL_CHICKEN_BIT;
+                       wrmsrl_safe(MSR_ZEN2_SPECTRAL_CHICKEN, value);
+               }
+       }
+}
+
 static void init_amd_zn(struct cpuinfo_x86 *c)
 {
        set_cpu_cap(c, X86_FEATURE_ZEN);
@@ -907,7 +927,8 @@ static void init_amd(struct cpuinfo_x86 *c)
        case 0x12: init_amd_ln(c); break;
        case 0x15: init_amd_bd(c); break;
        case 0x16: init_amd_jg(c); break;
-       case 0x17: fallthrough;
+       case 0x17: init_spectral_chicken(c);
+                  fallthrough;
        case 0x19: init_amd_zn(c); break;
        }
 

diff --git a/arch/x86/kernel/cpu/cpu.h b/arch/x86/kernel/cpu/cpu.h
index 2a8e584..7c9b589 100644 (file)
--- a/arch/x86/kernel/cpu/cpu.h
+++ b/arch/x86/kernel/cpu/cpu.h
@@ -61,6 +61,8 @@ static inline void tsx_init(void) { }
 static inline void tsx_ap_init(void) { }
 #endif /* CONFIG_CPU_SUP_INTEL */
 
+extern void init_spectral_chicken(struct cpuinfo_x86 *c);
+
 extern void get_cpu_cap(struct cpuinfo_x86 *c);
 extern void get_cpu_address_sizes(struct cpuinfo_x86 *c);
 extern void cpu_detect_cache_sizes(struct cpuinfo_x86 *c);

diff --git a/arch/x86/kernel/cpu/hygon.c b/arch/x86/kernel/cpu/hygon.c
index 3fcdda4..21fd425 100644 (file)
--- a/arch/x86/kernel/cpu/hygon.c
+++ b/arch/x86/kernel/cpu/hygon.c
@@ -302,6 +302,12 @@ static void init_hygon(struct cpuinfo_x86 *c)
        /* get apicid instead of initial apic id from cpuid */
        c->apicid = hard_smp_processor_id();
 
+       /*
+        * XXX someone from Hygon needs to confirm this DTRT
+        *
+       init_spectral_chicken(c);
+        */
+
        set_cpu_cap(c, X86_FEATURE_ZEN);
        set_cpu_cap(c, X86_FEATURE_CPB);