x86, pat/mtrr: Rendezvous all the cpus for MTRR/PAT init

SDM Vol 3a section titled "MTRR considerations in MP systems" specifies
the need for synchronizing the logical cpu's while initializing/updating
MTRR.

Currently Linux kernel does the synchronization of all cpu's only when
a single MTRR register is programmed/updated. During an AP online
(during boot/cpu-online/resume)  where we initialize all the MTRR/PAT registers,
we don't follow this synchronization algorithm.

This can lead to scenarios where during a dynamic cpu online, that logical cpu
is initializing MTRR/PAT with cache disabled (cr0.cd=1) etc while other logical
HT sibling continue to run (also with cache disabled because of cr0.cd=1
on its sibling).

Starting from Westmere, VMX transitions with cr0.cd=1 don't work properly
(because of some VMX performance optimizations) and the above scenario
(with one logical cpu doing VMX activity and another logical cpu coming online)
can result in system crash.

Fix the MTRR initialization by doing rendezvous of all the cpus. During
boot and resume, we delay the MTRR/PAT init for APs till all the
logical cpu's come online and the rendezvous process at the end of AP's bringup,
will initialize the MTRR/PAT for all AP's.

For dynamic single cpu online, we synchronize all the logical cpus and
do the MTRR/PAT init on the AP that is coming online.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 37 insertions, 9 deletions

diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
index 7af0f88a4163..7339be0aa580 100644
--- a/arch/x86/kernel/cpu/mtrr/main.c
+++ b/arch/x86/kernel/cpu/mtrr/main.c
@@ -58,6 +58,7 @@ unsigned int mtrr_usage_table[MTRR_MAX_VAR_RANGES];
 static DEFINE_MUTEX(mtrr_mutex);
 
 u64 size_or_mask, size_and_mask;
+u32 mtrr_aps_delayed_init;
 
 static struct mtrr_ops *mtrr_ops[X86_VENDOR_NUM];
 
@@ -163,7 +164,10 @@ static void ipi_handler(void *info)
         if (data->smp_reg != ~0U) {
                 mtrr_if->set(data->smp_reg, data->smp_base,
                              data->smp_size, data->smp_type);
-        } else {
+        } else if (mtrr_aps_delayed_init) {
+                /*
+                 * Initialize the MTRRs inaddition to the synchronisation.
+                 */
                 mtrr_if->set_all();
         }
 
@@ -265,6 +269,8 @@ set_mtrr(unsigned int reg, unsigned long base, unsigned long size, mtrr_type typ
          */
         if (reg != ~0U)
                 mtrr_if->set(reg, base, size, type);
+        else if (!mtrr_aps_delayed_init)
+                mtrr_if->set_all();
 
         /* Wait for the others */
         while (atomic_read(&data.count))
@@ -721,9 +727,7 @@ void __init mtrr_bp_init(void)
 
 void mtrr_ap_init(void)
 {
-        unsigned long flags;
-
-        if (!mtrr_if || !use_intel())
+        if (!use_intel() || mtrr_aps_delayed_init)
                 return;
         /*
          * Ideally we should hold mtrr_mutex here to avoid mtrr entries
@@ -738,11 +742,7 @@ void mtrr_ap_init(void)
          *   2. cpu hotadd time. We let mtrr_add/del_page hold cpuhotplug
          *      lock to prevent mtrr entry changes
          */
-        local_irq_save(flags);
-
-        mtrr_if->set_all();
-
-        local_irq_restore(flags);
+        set_mtrr(~0U, 0, 0, 0);
 }
 
 /**
@@ -753,6 +753,34 @@ void mtrr_save_state(void)
         smp_call_function_single(0, mtrr_save_fixed_ranges, NULL, 1);
 }
 
+void set_mtrr_aps_delayed_init(void)
+{
+        if (!use_intel())
+                return;
+
+        mtrr_aps_delayed_init = 1;
+}
+
+/*
+ * MTRR initialization for all AP's
+ */
+void mtrr_aps_init(void)
+{
+        if (!use_intel())
+                return;
+
+        set_mtrr(~0U, 0, 0, 0);
+        mtrr_aps_delayed_init = 0;
+}
+
+void mtrr_bp_restore(void)
+{
+        if (!use_intel())
+                return;
+
+        mtrr_if->set_all();
+}
+
 static int __init mtrr_init_finialize(void)
 {
         if (!mtrr_if)