commit
6690e86be83a ("sched/x86: Save [ER]FLAGS on context switch")
re-introduced the flags saving on context switch to prevent AC leakage.
The pushf/popf instructions are right among the callee saved register
section, so the comment explaining the save/restore is not entirely
correct.
Add a seperate comment to pushf/popf explaining the reason.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
pushl %ebx
pushl %edi
pushl %esi
+ /*
+ * Flags are saved to prevent AC leakage. This could go
+ * away if objtool would have 32bit support to verify
+ * the STAC/CLAC correctness.
+ */
pushfl
/* switch stack */
FILL_RETURN_BUFFER %ebx, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
#endif
- /* restore callee-saved registers */
+ /* Restore flags or the incoming task to restore AC state. */
popfl
+ /* restore callee-saved registers */
popl %esi
popl %edi
popl %ebx