x86/idle: Sanitize X86_BUG_AMD_E400 handling

amd_e400_idle(), the idle routine for AMD CPUs which are affected by
erratum 400 violates the RCU constraints by invoking tick_broadcast_enter()
and tick_broadcast_exit() after the core code has marked RCU non-idle.  The
functions can end up in lockdep or tracing, which rightfully triggers a
RCU warning.

The core code provides now a static branch conditional invocation of the
broadcast functions.

Remove amd_e400_idle(), enforce default_idle() and enable the static branch
on affected CPUs to cure this.

  [ bp: Fold in a fix for a IS_ENABLED() check fail missing a "CONFIG_"
    prefix which tglx spotted. ]

Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/877cim6sis.ffs@tglx

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 502986237cb65a9d4a6a301d3182b827254cba6b..080265369f8e9c14414cd957fb2fafc7eedcad4f 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -147,6 +147,7 @@ config X86
        select EDAC_ATOMIC_SCRUB
        select EDAC_SUPPORT
        select GENERIC_CLOCKEVENTS_BROADCAST    if X86_64 || (X86_32 && X86_LOCAL_APIC)
+       select GENERIC_CLOCKEVENTS_BROADCAST_IDLE       if GENERIC_CLOCKEVENTS_BROADCAST
        select GENERIC_CLOCKEVENTS_MIN_ADJUST
        select GENERIC_CMOS_UPDATE
        select GENERIC_CPU_AUTOPROBE

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 45a9d496fe2a0f04cbd2f753619c739b08f83fd4..b86ff0ffe59a0000e75a09fcf52a1267748fb8f4 100644 (file)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -845,31 +845,6 @@ void __noreturn stop_this_cpu(void *dummy)
        }
 }
 
-/*
- * AMD Erratum 400 aware idle routine. We handle it the same way as C3 power
- * states (local apic timer and TSC stop).
- *
- * XXX this function is completely buggered vs RCU and tracing.
- */
-static void amd_e400_idle(void)
-{
-       /*
-        * We cannot use static_cpu_has_bug() here because X86_BUG_AMD_APIC_C1E
-        * gets set after static_cpu_has() places have been converted via
-        * alternatives.
-        */
-       if (!boot_cpu_has_bug(X86_BUG_AMD_APIC_C1E)) {
-               default_idle();
-               return;
-       }
-
-       tick_broadcast_enter();
-
-       default_idle();
-
-       tick_broadcast_exit();
-}
-
 /*
  * Prefer MWAIT over HALT if MWAIT is supported, MWAIT_CPUID leaf
  * exists and whenever MONITOR/MWAIT extensions are present there is at
@@ -890,8 +865,8 @@ static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
        if (!cpu_has(c, X86_FEATURE_MWAIT))
                return 0;
 
-       /* Monitor has a bug. Fallback to HALT */
-       if (boot_cpu_has_bug(X86_BUG_MONITOR))
+       /* Monitor has a bug or APIC stops in C1E. Fallback to HALT */
+       if (boot_cpu_has_bug(X86_BUG_MONITOR) || boot_cpu_has_bug(X86_BUG_AMD_APIC_C1E))
                return 0;
 
        cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);
@@ -942,17 +917,15 @@ void select_idle_routine(const struct cpuinfo_x86 *c)
        if (x86_idle_set() || boot_option_idle_override == IDLE_POLL)
                return;
 
-       if (boot_cpu_has_bug(X86_BUG_AMD_E400)) {
-               pr_info("using AMD E400 aware idle routine\n");
-               static_call_update(x86_idle, amd_e400_idle);
-       } else if (prefer_mwait_c1_over_halt(c)) {
+       if (prefer_mwait_c1_over_halt(c)) {
                pr_info("using mwait in idle threads\n");
                static_call_update(x86_idle, mwait_idle);
        } else if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) {
                pr_info("using TDX aware idle routine\n");
                static_call_update(x86_idle, tdx_safe_halt);
-       } else
+       } else {
                static_call_update(x86_idle, default_idle);
+       }
 }
 
 void amd_e400_c1e_apic_setup(void)
@@ -985,7 +958,10 @@ void __init arch_post_acpi_subsys_init(void)
 
        if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC))
                mark_tsc_unstable("TSC halt in AMD C1E");
-       pr_info("System has AMD C1E enabled\n");
+
+       if (IS_ENABLED(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST_IDLE))
+               static_branch_enable(&arch_needs_tick_broadcast);
+       pr_info("System has AMD C1E erratum E400. Workaround enabled.\n");
 }
 
 static int __init idle_setup(char *str)