From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
[ Upstream commit d7caac991feeef1b871ee6988fd2c9725df09039 ]
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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/x86/include/asm/msr-index.h | 3 +++
arch/x86/kernel/cpu/amd.c | 23 ++++++++++++++++++++++-
arch/x86/kernel/cpu/cpu.h | 2 ++
arch/x86/kernel/cpu/hygon.c | 6 ++++++
4 files changed, 33 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index bd283cdd963a..0ff05c7882b2 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -553,6 +553,9 @@
/* 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 0c0b09796ced..8cf0659c0521 100644
--- 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 2a8e584fc991..7c9b5893c30a 100644
--- 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 3fcdda4c1e11..21fd425088fe 100644
--- 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);
--
2.35.1
