Re: [PATCH 2/8] x86, mce: remove redundant mce_available() checks

From: Borislav Petkov
Date: Fri Jun 17 2011 - 10:40:18 EST

On Fri, Jun 17, 2011 at 04:42:01AM -0400, Hidetoshi Seto wrote:
> I noticed that there is no need to check mce_available() on runtime.
> In fact we don't support asymmetric configuration such as mixture of
> varied processors which some are MCE capable while others are not.

simplify the above sentence please.

>
> Finally only 2 checks in init code path are enough for now.
>
> When !mce_available():
> - in mcheck_cpu_init():
> - mce timer is not initialized
... in __mcheck_cpu_init_timer()
> - cmci is not enabled
> - and later in mce_init_device():
> - sysfs files are not created
> - hotplug notifier is not registered
> So we don't need checks at all in these functions which is never

s/which is/because they are/

> called when !mce_available().
>
> For safety I also add a warning which is given when bad unsupported
> asymmetric configuration is detected.
>
> Signed-off-by: Hidetoshi Seto <seto.hidetoshi@xxxxxxxxxxxxxx>
> ---
> arch/x86/include/asm/mce.h | 2 -
> arch/x86/kernel/cpu/mcheck/mce.c | 34 ++++++++++---------------------
> arch/x86/kernel/cpu/mcheck/mce_intel.c | 2 +-
> 3 files changed, 12 insertions(+), 26 deletions(-)
>
> diff --git a/arch/x86/include/asm/mce.h b/arch/x86/include/asm/mce.h
> index 716b48a..77825dd 100644
> --- a/arch/x86/include/asm/mce.h
> +++ b/arch/x86/include/asm/mce.h
> @@ -180,8 +180,6 @@ void mce_amd_feature_init(struct cpuinfo_x86 *c);
> static inline void mce_amd_feature_init(struct cpuinfo_x86 *c) { }
> #endif
>
> -int mce_available(struct cpuinfo_x86 *c);
> -
> DECLARE_PER_CPU(unsigned, mce_exception_count);
> DECLARE_PER_CPU(unsigned, mce_poll_count);
>
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index 42fc8d2..205b334 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -449,7 +449,7 @@ static int mce_ring_add(unsigned long pfn)
> return 0;
> }
>
> -int mce_available(struct cpuinfo_x86 *c)
> +static int mce_available(struct cpuinfo_x86 *c)
> {
> if (mce_disabled)
> return 0;
> @@ -1121,10 +1121,7 @@ static void mce_start_timer(unsigned long data)
>
> WARN_ON(smp_processor_id() != data);
>
> - if (mce_available(__this_cpu_ptr(&cpu_info))) {
> - machine_check_poll(MCP_TIMESTAMP,
> - &__get_cpu_var(mce_poll_banks));
> - }
> + machine_check_poll(MCP_TIMESTAMP, &__get_cpu_var(mce_poll_banks));
>
> /*
> * Alert userspace if needed. If we logged an MCE, reduce the
> @@ -1146,8 +1143,7 @@ static void mce_timer_delete_all(void)
> int cpu;
>
> for_each_online_cpu(cpu) {
> - if (mce_available(&per_cpu(cpu_info, cpu)))
> - del_timer_sync(&per_cpu(mce_timer, cpu));
> + del_timer_sync(&per_cpu(mce_timer, cpu));
> }

no need for the parentheses but this should be part of the first patch
anyway.

> }
>
> @@ -1418,8 +1414,15 @@ void __cpuinit mcheck_cpu_init(struct cpuinfo_x86 *c)
> if (__mcheck_cpu_ancient_init(c))
> return;
>
> - if (!mce_available(c))
> + if (!mce_available(c)) {
> + /*
> + * Asymmetric configurations are not supported today.
> + * If mce_banks is allocated there must be a cpu passed here.
> + */
> + WARN_ON(!mce_disabled && mce_banks);
> + mce_disabled = 1;
> return;
> + }

I don't think this will ever happen so why complicate the code
needlessly? This can only be executed if at least one of the cores on
the system has CPUID(1)_EDX, bits 7 and 14 cleared and that's just
silly.

Besides, mcheck_init_device() already confirms we don't support
MCE-asymmetric configs:

if (!mce_available(&boot_cpu_data))
return -EIO;

> if (__mcheck_cpu_cap_init() < 0 || __mcheck_cpu_apply_quirks(c) < 0) {
> mce_disabled = 1;
> @@ -1761,8 +1764,6 @@ static struct syscore_ops mce_syscore_ops = {
>
> static void mce_cpu_restart(void *data)
> {
> - if (!mce_available(__this_cpu_ptr(&cpu_info)))
> - return;
> __mcheck_cpu_init_generic();
> __mcheck_cpu_init_timer();
> }
> @@ -1777,15 +1778,11 @@ static void mce_restart(void)
> /* Toggle features for corrected errors */
> static void mce_disable_cmci(void *data)
> {
> - if (!mce_available(__this_cpu_ptr(&cpu_info)))
> - return;
> cmci_clear();
> }
>
> static void mce_enable_ce(void *all)
> {
> - if (!mce_available(__this_cpu_ptr(&cpu_info)))
> - return;
> cmci_reenable();
> cmci_recheck();
> if (all)
> @@ -1946,9 +1943,6 @@ static __cpuinit int mce_sysdev_create(unsigned int cpu)
> int err;
> int i, j;
>
> - if (!mce_available(&boot_cpu_data))
> - return -EIO;
> -
> memset(&sysdev->kobj, 0, sizeof(struct kobject));
> sysdev->id = cpu;
> sysdev->cls = &mce_sysdev_class;
> @@ -2006,9 +2000,6 @@ static void __cpuinit mce_disable_cpu(void *h)
> unsigned long action = *(unsigned long *)h;
> int i;
>
> - if (!mce_available(__this_cpu_ptr(&cpu_info)))
> - return;
> -
> if (!(action & CPU_TASKS_FROZEN))
> cmci_clear();
> for (i = 0; i < banks; i++) {
> @@ -2024,9 +2015,6 @@ static void __cpuinit mce_reenable_cpu(void *h)
> unsigned long action = *(unsigned long *)h;
> int i;
>
> - if (!mce_available(__this_cpu_ptr(&cpu_info)))
> - return;
> -
> if (!(action & CPU_TASKS_FROZEN))
> cmci_reenable();
> for (i = 0; i < banks; i++) {
> diff --git a/arch/x86/kernel/cpu/mcheck/mce_intel.c b/arch/x86/kernel/cpu/mcheck/mce_intel.c
> index 8694ef5..393516c 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce_intel.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce_intel.c
> @@ -130,7 +130,7 @@ void cmci_recheck(void)
> unsigned long flags;
> int banks;
>
> - if (!mce_available(__this_cpu_ptr(&cpu_info)) || !cmci_supported(&banks))
> + if (!cmci_supported(&banks))
> return;
> local_irq_save(flags);
> machine_check_poll(MCP_TIMESTAMP, &__get_cpu_var(mce_banks_owned));
> --
> 1.7.1
>
>
>

--
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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