[Xen-changelog] [xen stable-4.10] x86/idle: Clear SPEC_CTRL while idle

[patchbot@xxxxxxx]

commit 3181472a5ca45ae5e77abbcf024d025d9ba79ced
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Feb 8 11:54:52 2018 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Feb 8 11:54:52 2018 +0100

    x86/idle: Clear SPEC_CTRL while idle
    
    On contemporary hardware, setting IBRS/STIBP has a performance impact on
    adjacent hyperthreads.  It is therefore recommended to clear the setting
    before becoming idle, to avoid an idle core preventing adjacent userspace
    execution from running at full performance.
    
    Care must be taken to ensure there are no ret or indirect branch 
instructions
    between spec_ctrl_{enter,exit}_idle() invocations, which are forced always
    inline.  Care must also be taken to avoid using spec_ctrl_enter_idle() 
between
    flushing caches and becoming idle, in cases where that matters.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 4c7e478d597b0346eef3a256cfd6794ac778b608
    master date: 2018-01-26 14:10:21 +0000
---
 xen/arch/x86/acpi/cpu_idle.c    | 21 +++++++++++++++++++++
 xen/arch/x86/cpu/mwait-idle.c   |  7 +++++++
 xen/arch/x86/domain.c           |  8 ++++++++
 xen/include/asm-x86/spec_ctrl.h | 34 ++++++++++++++++++++++++++++++++++
 4 files changed, 70 insertions(+)

diff --git a/xen/arch/x86/acpi/cpu_idle.c b/xen/arch/x86/acpi/cpu_idle.c
index b605a87..5feda70 100644
--- a/xen/arch/x86/acpi/cpu_idle.c
+++ b/xen/arch/x86/acpi/cpu_idle.c
@@ -55,6 +55,7 @@
 #include <asm/mwait.h>
 #include <xen/notifier.h>
 #include <xen/cpu.h>
+#include <asm/spec_ctrl.h>
 
 /*#define DEBUG_PM_CX*/
 
@@ -417,8 +418,14 @@ void mwait_idle_with_hints(unsigned int eax, unsigned int 
ecx)
      */
     if ( (expires > NOW() || expires == 0) && !softirq_pending(cpu) )
     {
+        struct cpu_info *info = get_cpu_info();
+
         cpumask_set_cpu(cpu, &cpuidle_mwait_flags);
+
+        spec_ctrl_enter_idle(info);
         __mwait(eax, ecx);
+        spec_ctrl_exit_idle(info);
+
         cpumask_clear_cpu(cpu, &cpuidle_mwait_flags);
     }
 
@@ -433,6 +440,8 @@ static void acpi_processor_ffh_cstate_enter(struct 
acpi_processor_cx *cx)
 
 static void acpi_idle_do_entry(struct acpi_processor_cx *cx)
 {
+    struct cpu_info *info = get_cpu_info();
+
     switch ( cx->entry_method )
     {
     case ACPI_CSTATE_EM_FFH:
@@ -440,15 +449,19 @@ static void acpi_idle_do_entry(struct acpi_processor_cx 
*cx)
         acpi_processor_ffh_cstate_enter(cx);
         return;
     case ACPI_CSTATE_EM_SYSIO:
+        spec_ctrl_enter_idle(info);
         /* IO port based C-state */
         inb(cx->address);
         /* Dummy wait op - must do something useless after P_LVL2 read
            because chipsets cannot guarantee that STPCLK# signal
            gets asserted in time to freeze execution properly. */
         inl(pmtmr_ioport);
+        spec_ctrl_exit_idle(info);
         return;
     case ACPI_CSTATE_EM_HALT:
+        spec_ctrl_enter_idle(info);
         safe_halt();
+        spec_ctrl_exit_idle(info);
         local_irq_disable();
         return;
     }
@@ -576,7 +589,13 @@ static void acpi_processor_idle(void)
         if ( pm_idle_save )
             pm_idle_save();
         else
+        {
+            struct cpu_info *info = get_cpu_info();
+
+            spec_ctrl_enter_idle(info);
             safe_halt();
+            spec_ctrl_exit_idle(info);
+        }
         return;
     }
 
@@ -755,6 +774,7 @@ void acpi_dead_idle(void)
          * Otherwise, CPU may still hold dirty data, breaking cache coherency,
          * leading to strange errors.
          */
+        spec_ctrl_enter_idle(get_cpu_info());
         wbinvd();
 
         while ( 1 )
@@ -784,6 +804,7 @@ void acpi_dead_idle(void)
         u32 address = cx->address;
         u32 pmtmr_ioport_local = pmtmr_ioport;
 
+        spec_ctrl_enter_idle(get_cpu_info());
         wbinvd();
 
         while ( 1 )
diff --git a/xen/arch/x86/cpu/mwait-idle.c b/xen/arch/x86/cpu/mwait-idle.c
index 762dff1..e357f29 100644
--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -58,6 +58,7 @@
 #include <asm/hpet.h>
 #include <asm/mwait.h>
 #include <asm/msr.h>
+#include <asm/spec_ctrl.h>
 #include <acpi/cpufreq/cpufreq.h>
 
 #define MWAIT_IDLE_VERSION "0.4.1"
@@ -736,7 +737,13 @@ static void mwait_idle(void)
                if (pm_idle_save)
                        pm_idle_save();
                else
+               {
+                       struct cpu_info *info = get_cpu_info();
+
+                       spec_ctrl_enter_idle(info);
                        safe_halt();
+                       spec_ctrl_exit_idle(info);
+               }
                return;
        }
 
diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 8e936c8..7e10a2a 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -55,6 +55,7 @@
 #include <asm/hvm/viridian.h>
 #include <asm/debugreg.h>
 #include <asm/msr.h>
+#include <asm/spec_ctrl.h>
 #include <asm/traps.h>
 #include <asm/nmi.h>
 #include <asm/mce.h>
@@ -75,9 +76,15 @@ void (*dead_idle) (void) __read_mostly = default_dead_idle;
 
 static void default_idle(void)
 {
+    struct cpu_info *info = get_cpu_info();
+
     local_irq_disable();
     if ( cpu_is_haltable(smp_processor_id()) )
+    {
+        spec_ctrl_enter_idle(info);
         safe_halt();
+        spec_ctrl_exit_idle(info);
+    }
     else
         local_irq_enable();
 }
@@ -89,6 +96,7 @@ void default_dead_idle(void)
      * held by the CPUs spinning here indefinitely, and get discarded by
      * a subsequent INIT.
      */
+    spec_ctrl_enter_idle(get_cpu_info());
     wbinvd();
     for ( ; ; )
         halt();
diff --git a/xen/include/asm-x86/spec_ctrl.h b/xen/include/asm-x86/spec_ctrl.h
index e328b0f..5ab4ff3 100644
--- a/xen/include/asm-x86/spec_ctrl.h
+++ b/xen/include/asm-x86/spec_ctrl.h
@@ -20,7 +20,9 @@
 #ifndef __X86_SPEC_CTRL_H__
 #define __X86_SPEC_CTRL_H__
 
+#include <asm/alternative.h>
 #include <asm/current.h>
+#include <asm/msr-index.h>
 
 void init_speculation_mitigations(void);
 
@@ -35,6 +37,38 @@ static inline void init_shadow_spec_ctrl_state(void)
     info->bti_ist_info = default_bti_ist_info;
 }
 
+/* WARNING! `ret`, `call *`, `jmp *` not safe after this call. */
+static always_inline void spec_ctrl_enter_idle(struct cpu_info *info)
+{
+    uint32_t val = 0;
+
+    /*
+     * Latch the new shadow value, then enable shadowing, then update the MSR.
+     * There are no SMP issues here; only local processor ordering concerns.
+     */
+    info->shadow_spec_ctrl = val;
+    barrier();
+    info->use_shadow_spec_ctrl = true;
+    barrier();
+    asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_XEN_IBRS_SET)
+                   :: "a" (val), "c" (MSR_SPEC_CTRL), "d" (0) : "memory" );
+}
+
+/* WARNING! `ret`, `call *`, `jmp *` not safe before this call. */
+static always_inline void spec_ctrl_exit_idle(struct cpu_info *info)
+{
+    uint32_t val = SPEC_CTRL_IBRS;
+
+    /*
+     * Disable shadowing before updating the MSR.  There are no SMP issues
+     * here; only local processor ordering concerns.
+     */
+    info->use_shadow_spec_ctrl = false;
+    barrier();
+    asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_XEN_IBRS_SET)
+                   :: "a" (val), "c" (MSR_SPEC_CTRL), "d" (0) : "memory" );
+}
+
 #endif /* !__X86_SPEC_CTRL_H__ */
 
 /*
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.10

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