x86/entry/32: Clarify register saving in __switch_to_asm() (a3ba9660) · Commits · 戴 / test

commit ("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>

arch/x86/entry/entry_32.S

+7 −1

Original line number	Diff line number	Diff line
		@@ -718,6 +718,11 @@ ENTRY(__switch_to_asm)
		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 */
		@@ -740,8 +745,9 @@ ENTRY(__switch_to_asm)
		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

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