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x86/cpu/amd: Add Spectral Chicken

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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>
This commit is contained in:
Peter Zijlstra 2022-06-14 23:16:04 +02:00 committed by Borislav Petkov
parent a09a6e2399
commit d7caac991f
4 changed files with 33 additions and 1 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

3
arch/x86/include/asm/msr-index.h
View file

@ -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

23
arch/x86/kernel/cpu/amd.c
View file

@ -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;
}

2
arch/x86/kernel/cpu/cpu.h
View file

@ -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);

6
arch/x86/kernel/cpu/hygon.c
View file

@ -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);