Re: [PATCH v3 08/10] x86/mtrr: let cache_aps_delayed_init replace mtrr_aps_delayed_init

[Borislav Petkov <bp@xxxxxxxxx>]

On Tue, Sep 27, 2022 at 02:21:17PM +0200, Juergen Gross wrote:
> So replacing the bool with "(system_state != SYSTEM_RUNNING)" is fine
> with you right now? We can later switch that to the "more elegant"
> solution when it shows up.

Ok, I think I have something. And it was staring me straight in the
face but I didn't see it: the MTRR code needs a hotplug notifier. In
that notifier it can do the immediate, i.e., non-delayed init while the
delayed init becomes the default, see below.

And ignore the pr_info debugging gunk pls.

mtrr_ap_init() becomes the notifier callback. It doesn't need to be
called in identify_secondary_cpu() anymore as in the init case that
function doesn't do anything - delayed=true - and in the hotplug case
the notifier runs.

mtrr_aps_init() - "aps" in plural - does the delayed init after all CPUs
have been brought online after the box has booted. That might need some
renaming.

And yes, there's a lot more to cleanup after this. This code has grown
wart after wart over the years...

Fun.

---
diff --git a/arch/x86/include/asm/mtrr.h b/arch/x86/include/asm/mtrr.h
index 76d726074c16..1a3dad244bba 100644
--- a/arch/x86/include/asm/mtrr.h
+++ b/arch/x86/include/asm/mtrr.h
@@ -42,8 +42,6 @@ extern int mtrr_add_page(unsigned long base, unsigned long 
size,
 extern int mtrr_del(int reg, unsigned long base, unsigned long size);
 extern int mtrr_del_page(int reg, unsigned long base, unsigned long size);
 extern void mtrr_centaur_report_mcr(int mcr, u32 lo, u32 hi);
-extern void mtrr_ap_init(void);
-extern void set_mtrr_aps_delayed_init(void);
 extern void mtrr_aps_init(void);
 extern void mtrr_bp_restore(void);
 extern int mtrr_trim_uncached_memory(unsigned long end_pfn);
@@ -83,8 +81,6 @@ static inline int mtrr_trim_uncached_memory(unsigned long 
end_pfn)
 static inline void mtrr_centaur_report_mcr(int mcr, u32 lo, u32 hi)
 {
 }
-#define mtrr_ap_init() do {} while (0)
-#define set_mtrr_aps_delayed_init() do {} while (0)
 #define mtrr_aps_init() do {} while (0)
 #define mtrr_bp_restore() do {} while (0)
 #  endif
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 3e508f239098..deef1b5b27cc 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1948,7 +1948,6 @@ void identify_secondary_cpu(struct cpuinfo_x86 *c)
 #ifdef CONFIG_X86_32
        enable_sep_cpu();
 #endif
-       mtrr_ap_init();
        validate_apic_and_package_id(c);
        x86_spec_ctrl_setup_ap();
        update_srbds_msr();
diff --git a/arch/x86/kernel/cpu/mtrr/mtrr.c b/arch/x86/kernel/cpu/mtrr/mtrr.c
index 2746cac9d8a9..abbf7cb8a430 100644
--- a/arch/x86/kernel/cpu/mtrr/mtrr.c
+++ b/arch/x86/kernel/cpu/mtrr/mtrr.c
@@ -69,7 +69,6 @@ unsigned int mtrr_usage_table[MTRR_MAX_VAR_RANGES];
 static DEFINE_MUTEX(mtrr_mutex);
 
 u64 size_or_mask, size_and_mask;
-static bool mtrr_aps_delayed_init;
 
 static const struct mtrr_ops *mtrr_ops[X86_VENDOR_NUM] __ro_after_init;
 
@@ -176,7 +175,7 @@ static int mtrr_rendezvous_handler(void *info)
        if (data->smp_reg != ~0U) {
                mtrr_if->set(data->smp_reg, data->smp_base,
                             data->smp_size, data->smp_type);
-       } else if (mtrr_aps_delayed_init || !cpu_online(smp_processor_id())) {
+       } else if (!cpu_online(smp_processor_id())) {
                mtrr_if->set_all();
        }
        return 0;
@@ -784,13 +783,16 @@ void __init mtrr_bp_init(void)
        }
 }
 
-void mtrr_ap_init(void)
+static int mtrr_ap_init(unsigned int cpu)
 {
+       pr_info("%s: single AP entry, use_intel: %d, mtrr_enabled: %d, 
mtrr_aps_delayed_init\n",
+               __func__, use_intel(), mtrr_enabled());
+
        if (!mtrr_enabled())
-               return;
+               return 1;
 
-       if (!use_intel() || mtrr_aps_delayed_init)
-               return;
+       if (!use_intel())
+               return 1;
 
        /*
         * Ideally we should hold mtrr_mutex here to avoid mtrr entries
@@ -806,6 +808,8 @@ void mtrr_ap_init(void)
         *      lock to prevent mtrr entry changes
         */
        set_mtrr_from_inactive_cpu(~0U, 0, 0, 0);
+
+       return 0;
 }
 
 /**
@@ -820,37 +824,24 @@ void mtrr_save_state(void)
                return;
 
        first_cpu = cpumask_first(cpu_online_mask);
-       smp_call_function_single(first_cpu, mtrr_save_fixed_ranges, NULL, 1);
-}
 
-void set_mtrr_aps_delayed_init(void)
-{
-       if (!mtrr_enabled())
-               return;
-       if (!use_intel())
-               return;
+       pr_info("%s: first_cpu: %d\n", __func__, first_cpu);
 
-       mtrr_aps_delayed_init = true;
+       smp_call_function_single(first_cpu, mtrr_save_fixed_ranges, NULL, 1);
 }
 
 /*
- * Delayed MTRR initialization for all AP's
+ * Delayed MTRR initialization for all APs
  */
 void mtrr_aps_init(void)
 {
-       if (!use_intel() || !mtrr_enabled())
-               return;
+       pr_info("%s: entry, use_intel: %d, mtrr_enabled: %d, 
mtrr_aps_delayed_init\n",
+               __func__, use_intel(), mtrr_enabled());
 
-       /*
-        * Check if someone has requested the delay of AP MTRR initialization,
-        * by doing set_mtrr_aps_delayed_init(), prior to this point. If not,
-        * then we are done.
-        */
-       if (!mtrr_aps_delayed_init)
+       if (!use_intel() || !mtrr_enabled())
                return;
 
        set_mtrr(~0U, 0, 0, 0);
-       mtrr_aps_delayed_init = false;
 }
 
 void mtrr_bp_restore(void)
@@ -869,6 +860,10 @@ static int __init mtrr_init_finialize(void)
        if (use_intel()) {
                if (!changed_by_mtrr_cleanup)
                        mtrr_state_warn();
+
+               cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, 
"x86/mtrr:online",
+                                 mtrr_ap_init, NULL);
+
                return 0;
        }
 
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index f24227bc3220..171acef35201 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1428,7 +1428,7 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 
        uv_system_init();
 
-       set_mtrr_aps_delayed_init();
+       pr_info("%s: set_mtrr_aps_delayed_init\n", __func__);
 
        smp_quirk_init_udelay();
 
@@ -1439,7 +1439,7 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 
 void arch_thaw_secondary_cpus_begin(void)
 {
-       set_mtrr_aps_delayed_init();
+       pr_info("%s: set_mtrr_aps_delayed_init\n", __func__);
 }
 
 void arch_thaw_secondary_cpus_end(void)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index bbad5e375d3b..fc14601b908c 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -591,6 +591,8 @@ static int bringup_cpu(unsigned int cpu)
        struct task_struct *idle = idle_thread_get(cpu);
        int ret;
 
+       pr_info("%s: CPU%d\n", __func__, cpu);
+
        /*
         * Reset stale stack state from the last time this CPU was online.
         */


-- 
Regards/Gruss,
    Boris.

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