Re: [PATCH -final] x86/clear_user: Make it faster

[Alexey Dobriyan]

On Tue, Jul 05, 2022 at 07:01:06PM +0200, Borislav Petkov wrote:

> +	asm volatile(
> +		"1:\n\t"
> +		ALTERNATIVE_3("rep stosb",
> +			      "call clear_user_erms",	  ALT_NOT(X86_FEATURE_FSRM),
> +			      "call clear_user_rep_good", ALT_NOT(X86_FEATURE_ERMS),
> +			      "call clear_user_original", ALT_NOT(X86_FEATURE_REP_GOOD))
> +		"2:\n"
> +	       _ASM_EXTABLE_UA(1b, 2b)
> +	       : "+&c" (size), "+&D" (addr), ASM_CALL_CONSTRAINT
> +	       : "a" (0)
> +		/* rep_good clobbers %rdx */
> +	       : "rdx");

"+c" and "+D" should be enough for 1 instruction assembly?