[Xen-changelog] [xen staging] x86/microcode: remove microcode_update_lock

[patchbot@xxxxxxx]

commit 487b49e08ab103353ad57cdca004999383552738
Author:     Chao Gao <chao.gao@xxxxxxxxx>
AuthorDate: Fri Sep 27 14:19:38 2019 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Sep 27 14:19:38 2019 +0200

    x86/microcode: remove microcode_update_lock
    
    microcode_update_lock is to prevent logic threads of a same core from
    updating microcode at the same time. But due to using a global lock, it
    also prevented parallel microcode updating on different cores.
    
    Remove this lock in order to update microcode in parallel. It is safe
    because we have already ensured serialization of sibling threads at the
    caller side.
    1.For late microcode update, do_microcode_update() ensures that only one
      sibiling thread of a core can update microcode.
    2.For microcode update during system startup or CPU-hotplug,
      microcode_mutex() guarantees update serialization of logical threads.
    3.get/put_cpu_bitmaps() prevents the concurrency of CPU-hotplug and
      late microcode update.
    
    Note that printk in apply_microcode() and svm_host_osvm_init() (for AMD
    only) are still processed sequentially.
    
    Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/microcode_amd.c   | 8 +-------
 xen/arch/x86/microcode_intel.c | 8 +-------
 2 files changed, 2 insertions(+), 14 deletions(-)

diff --git a/xen/arch/x86/microcode_amd.c b/xen/arch/x86/microcode_amd.c
index 9a8f179dc6..1e52f7f49a 100644
--- a/xen/arch/x86/microcode_amd.c
+++ b/xen/arch/x86/microcode_amd.c
@@ -74,9 +74,6 @@ struct mpbhdr {
     uint8_t data[];
 };
 
-/* serialize access to the physical write */
-static DEFINE_SPINLOCK(microcode_update_lock);
-
 /* See comment in start_update() for cases when this routine fails */
 static int collect_cpu_info(struct cpu_signature *csig)
 {
@@ -232,7 +229,6 @@ static enum microcode_match_result compare_patch(
 
 static int apply_microcode(const struct microcode_patch *patch)
 {
-    unsigned long flags;
     uint32_t rev;
     int hw_err;
     unsigned int cpu = smp_processor_id();
@@ -247,15 +243,13 @@ static int apply_microcode(const struct microcode_patch 
*patch)
 
     hdr = patch->mc_amd->mpb;
 
-    spin_lock_irqsave(&microcode_update_lock, flags);
+    BUG_ON(local_irq_is_enabled());
 
     hw_err = wrmsr_safe(MSR_AMD_PATCHLOADER, (unsigned long)hdr);
 
     /* get patch id after patching */
     rdmsrl(MSR_AMD_PATCHLEVEL, rev);
 
-    spin_unlock_irqrestore(&microcode_update_lock, flags);
-
     /*
      * Some processors leave the ucode blob mapping as UC after the update.
      * Flush the mapping to regain normal cacheability.
diff --git a/xen/arch/x86/microcode_intel.c b/xen/arch/x86/microcode_intel.c
index c083e1752f..9ededcc73a 100644
--- a/xen/arch/x86/microcode_intel.c
+++ b/xen/arch/x86/microcode_intel.c
@@ -93,9 +93,6 @@ struct extended_sigtable {
 
 #define exttable_size(et) ((et)->count * EXT_SIGNATURE_SIZE + EXT_HEADER_SIZE)
 
-/* serialize access to the physical write to MSR 0x79 */
-static DEFINE_SPINLOCK(microcode_update_lock);
-
 static int collect_cpu_info(struct cpu_signature *csig)
 {
     unsigned int cpu_num = smp_processor_id();
@@ -287,7 +284,6 @@ static enum microcode_match_result compare_patch(
 
 static int apply_microcode(const struct microcode_patch *patch)
 {
-    unsigned long flags;
     uint64_t msr_content;
     unsigned int val[2];
     unsigned int cpu_num = raw_smp_processor_id();
@@ -302,8 +298,7 @@ static int apply_microcode(const struct microcode_patch 
*patch)
 
     mc_intel = patch->mc_intel;
 
-    /* serialize access to the physical write to MSR 0x79 */
-    spin_lock_irqsave(&microcode_update_lock, flags);
+    BUG_ON(local_irq_is_enabled());
 
     /* write microcode via MSR 0x79 */
     wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)mc_intel->bits);
@@ -316,7 +311,6 @@ static int apply_microcode(const struct microcode_patch 
*patch)
     rdmsrl(MSR_IA32_UCODE_REV, msr_content);
     val[1] = (uint32_t)(msr_content >> 32);
 
-    spin_unlock_irqrestore(&microcode_update_lock, flags);
     if ( val[1] != mc_intel->hdr.rev )
     {
         printk(KERN_ERR "microcode: CPU%d update from revision "
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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