x86/process: Move the buffer clearing before MONITOR

Commit 8e786a85c0a3c0fffae6244733fb576eeabd9dec upstream.

Move the VERW clearing before the MONITOR so that VERW doesn't disarm it
and the machine never enters C1.

Original idea by Kim Phillips <kim.phillips@amd.com>.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index 2c6020729dd145d9a25e1a83ebedba45470f8400..d938792c11d97954f1281fc66a80b959d5bbe50a 100644 (file)
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -44,8 +44,6 @@ static inline void __monitorx(const void *eax, unsigned long ecx,
 
 static inline void __mwait(unsigned long eax, unsigned long ecx)
 {
-       x86_idle_clear_cpu_buffers();
-
        /* "mwait %eax, %ecx;" */
        asm volatile(".byte 0x0f, 0x01, 0xc9;"
                     :: "a" (eax), "c" (ecx));
@@ -89,7 +87,6 @@ static inline void __mwaitx(unsigned long eax, unsigned long ebx,
 
 static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
 {
-       x86_idle_clear_cpu_buffers();
 
        /* "mwait %eax, %ecx;" */
        asm volatile("sti; .byte 0x0f, 0x01, 0xc9;"
@@ -108,6 +105,11 @@ static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
  */
 static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
 {
+       if (need_resched())
+               return;
+
+       x86_idle_clear_cpu_buffers();
+
        if (static_cpu_has_bug(X86_BUG_MONITOR) || !current_set_polling_and_test()) {
                if (static_cpu_has_bug(X86_BUG_CLFLUSH_MONITOR)) {
                        mb();
@@ -116,9 +118,13 @@ static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
                }
 
                __monitor((void *)&current_thread_info()->flags, 0, 0);
-               if (!need_resched())
-                       __mwait(eax, ecx);
+               if (need_resched())
+                       goto out;
+
+               __mwait(eax, ecx);
        }
+
+out:
        current_clr_polling();
 }
 

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 50fe793498994d68c98092bc765a04dccb566295..1138b999cb14b2879583331a1744babb6ee137bc 100644 (file)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -887,6 +887,11 @@ static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
  */
 static __cpuidle void mwait_idle(void)
 {
+       if (need_resched())
+               return;
+
+       x86_idle_clear_cpu_buffers();
+
        if (!current_set_polling_and_test()) {
                if (this_cpu_has(X86_BUG_CLFLUSH_MONITOR)) {
                        mb(); /* quirk */
@@ -895,13 +900,17 @@ static __cpuidle void mwait_idle(void)
                }
 
                __monitor((void *)&current_thread_info()->flags, 0, 0);
-               if (!need_resched())
-                       __sti_mwait(0, 0);
-               else
+               if (need_resched()) {
                        raw_local_irq_enable();
+                       goto out;
+               }
+
+               __sti_mwait(0, 0);
        } else {
                raw_local_irq_enable();
        }
+
+out:
        __current_clr_polling();
 }