1 files changed, 8 insertions, 4 deletions

diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index d7f3b3b78ac3..751bf4b7bf11 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -79,12 +79,12 @@ do {									\
 #else /* CONFIG_X86_32 */
 
 /* frame pointer must be last for get_wchan */
-#define SAVE_CONTEXT    "pushf ; pushq %%rbp ; movq %%rsi,%%rbp\n\t"
-#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp ; popf\t"
+#define SAVE_CONTEXT    "pushq %%rbp ; movq %%rsi,%%rbp\n\t"
+#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp\t"
 
 #define __EXTRA_CLOBBER  \
         , "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \
-          "r12", "r13", "r14", "r15"
+          "r12", "r13", "r14", "r15", "flags"
 
 #ifdef CONFIG_CC_STACKPROTECTOR
 #define __switch_canary                                                   \
@@ -100,7 +100,11 @@ do {									\
 #define __switch_canary_iparam
 #endif  /* CC_STACKPROTECTOR */
 
-/* Save restore flags to clear handle leaking NT */
+/*
+ * There is no need to save or restore flags, because flags are always
+ * clean in kernel mode, with the possible exception of IOPL.  Kernel IOPL
+ * has no effect.
+ */
 #define switch_to(prev, next, last) \
         asm volatile(SAVE_CONTEXT                                         \
              "movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */       \