[Xen-changelog] [xen master] xen/x86: Fix cflush()'s parameter tracking

[patchbot@xxxxxxx]

commit cc56d87dc3e203a5701f21fb3a81f347cf0ae9eb
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Mar 15 12:28:46 2019 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Mar 15 14:36:07 2019 +0000

    xen/x86: Fix cflush()'s parameter tracking
    
    Forcing a register operand hides (from the compiler) the fact that clflush
    behaves as a read from the memory operand (wrt memory order, faults, etc.).
    It also reduces the compilers flexibility with register scheduling.
    
    Re-implement clfush() (and wbinvd() for consistency) as a static inline 
rather
    than a macro, and have it take a const void pointer.
    
    In practice, the only generated code which gets modified by this is in
    mwait_idle_with_hints(), where a disp8 encoding now gets used.
    
    While here, I noticed that &mwait_wakeup(cpu) was being calculated twice.
    This is caused by the memory clobber in mb(), so take the opportunity to 
help
    the optimiser by calculating it once, ahead of time.  bloat-o-meter reports 
a
    delta of -26 as a result of this change.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/acpi/cpu_idle.c |  5 +++--
 xen/include/asm-x86/system.h | 12 ++++++++----
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/acpi/cpu_idle.c b/xen/arch/x86/acpi/cpu_idle.c
index 14b02789c5..654de24f40 100644
--- a/xen/arch/x86/acpi/cpu_idle.c
+++ b/xen/arch/x86/acpi/cpu_idle.c
@@ -401,15 +401,16 @@ void mwait_idle_with_hints(unsigned int eax, unsigned int 
ecx)
 {
     unsigned int cpu = smp_processor_id();
     s_time_t expires = per_cpu(timer_deadline, cpu);
+    const void *monitor_addr = &mwait_wakeup(cpu);
 
     if ( boot_cpu_has(X86_FEATURE_CLFLUSH_MONITOR) )
     {
         mb();
-        clflush((void *)&mwait_wakeup(cpu));
+        clflush(monitor_addr);
         mb();
     }
 
-    __monitor((void *)&mwait_wakeup(cpu), 0, 0);
+    __monitor(monitor_addr, 0, 0);
     smp_mb();
 
     /*
diff --git a/xen/include/asm-x86/system.h b/xen/include/asm-x86/system.h
index c665499e36..3246797bec 100644
--- a/xen/include/asm-x86/system.h
+++ b/xen/include/asm-x86/system.h
@@ -11,11 +11,15 @@
     __sel;                                                      \
 })
 
-#define wbinvd() \
-    asm volatile ( "wbinvd" : : : "memory" )
+static inline void wbinvd(void)
+{
+    asm volatile ( "wbinvd" ::: "memory" );
+}
 
-#define clflush(a) \
-    asm volatile ( "clflush (%0)" : : "r"(a) )
+static inline void clflush(const void *p)
+{
+    asm volatile ( "clflush %0" :: "m" (*(const char *)p) );
+}
 
 #define xchg(ptr,v) \
     ((__typeof__(*(ptr)))__xchg((unsigned long)(v),(ptr),sizeof(*(ptr))))
--
generated by git-patchbot for /home/xen/git/xen.git#master

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