From ef265d7551ee39038b8b2a7f158cdb0d141e2863 Mon Sep 17 00:00:00 2001
From: Jan Beulich <jbeulich@suse.com>
Date: Wed, 18 Sep 2019 15:12:33 +0200
Subject: [PATCH] core-parking: interact with runtime SMT-disabling

When disabling SMT at runtime, secondary threads should no longer be
candidates for bringing back up in response to _PUR ACPI events. Purge
them from the tracking array.

Doing so involves adding locking to guard accounting data in the core
parking code. While adding the declaration for the lock, take the
liberty to drop two unnecessary forward function declarations.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
 xen/arch/x86/sysctl.c     |  3 +++
 xen/common/core_parking.c | 57 ++++++++++++++++++++++++++++++---------
 xen/include/asm-x86/smp.h |  1 +
 3 files changed, 49 insertions(+), 12 deletions(-)

diff --git a/xen/arch/x86/sysctl.c b/xen/arch/x86/sysctl.c
index 50be0c722a..3742ede61b 100644
--- a/xen/arch/x86/sysctl.c
+++ b/xen/arch/x86/sysctl.c
@@ -128,6 +128,9 @@ static long smt_up_down_helper(void *data)
         if ( !(x86_cpu_to_apicid[cpu] & sibling_mask) )
             continue;
 
+        if ( !up && core_parking_remove(cpu) )
+            continue;
+
         ret = up ? cpu_up_helper(_p(cpu))
                  : cpu_down_helper(_p(cpu));
 
diff --git a/xen/common/core_parking.c b/xen/common/core_parking.c
index c22710f94d..a6669e1766 100644
--- a/xen/common/core_parking.c
+++ b/xen/common/core_parking.c
@@ -25,9 +25,7 @@
 #define CORE_PARKING_INCREMENT 1
 #define CORE_PARKING_DECREMENT 2
 
-static unsigned int core_parking_power(unsigned int event);
-static unsigned int core_parking_performance(unsigned int event);
-
+static DEFINE_SPINLOCK(accounting_lock);
 static uint32_t cur_idle_nums;
 static unsigned int core_parking_cpunum[NR_CPUS] = {[0 ... NR_CPUS-1] = -1};
 
@@ -100,10 +98,10 @@ static unsigned int core_parking_performance(unsigned int event)
     break;
 
     case CORE_PARKING_DECREMENT:
-    {
-        cpu = core_parking_cpunum[cur_idle_nums -1];
-    }
-    break;
+        spin_lock(&accounting_lock);
+        cpu = core_parking_cpunum[cur_idle_nums - 1];
+        spin_unlock(&accounting_lock);
+        break;
 
     default:
         break;
@@ -158,10 +156,10 @@ static unsigned int core_parking_power(unsigned int event)
     break;
 
     case CORE_PARKING_DECREMENT:
-    {
-        cpu = core_parking_cpunum[cur_idle_nums -1];
-    }
-    break;
+        spin_lock(&accounting_lock);
+        cpu = core_parking_cpunum[cur_idle_nums - 1];
+        spin_unlock(&accounting_lock);
+        break;
 
     default:
         break;
@@ -185,7 +183,11 @@ long core_parking_helper(void *data)
         ret = cpu_down(cpu);
         if ( ret )
             return ret;
+
+        spin_lock(&accounting_lock);
+        BUG_ON(cur_idle_nums >= ARRAY_SIZE(core_parking_cpunum));
         core_parking_cpunum[cur_idle_nums++] = cpu;
+        spin_unlock(&accounting_lock);
     }
 
     while ( cur_idle_nums > idle_nums )
@@ -194,12 +196,43 @@ long core_parking_helper(void *data)
         ret = cpu_up(cpu);
         if ( ret )
             return ret;
-        core_parking_cpunum[--cur_idle_nums] = -1;
+
+        if ( !core_parking_remove(cpu) )
+        {
+            ret = cpu_down(cpu);
+            if ( ret == -EEXIST )
+                ret = 0;
+            if ( ret )
+                break;
+        }
     }
 
     return ret;
 }
 
+bool core_parking_remove(unsigned int cpu)
+{
+    unsigned int i;
+    bool found = false;
+
+    spin_lock(&accounting_lock);
+
+    for ( i = 0; i < cur_idle_nums; ++i )
+        if ( core_parking_cpunum[i] == cpu )
+        {
+            found = true;
+            --cur_idle_nums;
+            break;
+        }
+
+    for ( ; i < cur_idle_nums; ++i )
+        core_parking_cpunum[i] = core_parking_cpunum[i + 1];
+
+    spin_unlock(&accounting_lock);
+
+    return found;
+}
+
 uint32_t get_cur_idle_nums(void)
 {
     return cur_idle_nums;
diff --git a/xen/include/asm-x86/smp.h b/xen/include/asm-x86/smp.h
index 9f533f9072..61446d0efd 100644
--- a/xen/include/asm-x86/smp.h
+++ b/xen/include/asm-x86/smp.h
@@ -63,6 +63,7 @@ long cpu_up_helper(void *data);
 long cpu_down_helper(void *data);
 
 long core_parking_helper(void *data);
+bool core_parking_remove(unsigned int cpu);
 uint32_t get_cur_idle_nums(void);
 
 /*
-- 
2.30.2