linux-kernel - Re: [PATCH 07/13] x86/paravirt: Simplify ____PVOP

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Date:   Wed, 22 Nov 2017 17:35:46 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Juergen Gross <jgross@...e.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <alexander.levin@...izon.com>,
        live-patching@...r.kernel.org, Jiri Slaby <jslaby@...e.cz>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mike Galbraith <efault@....de>,
        Chris Wright <chrisw@...s-sol.org>,
        Alok Kataria <akataria@...are.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        virtualization@...ts.linux-foundation.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 07/13] x86/paravirt: Simplify ____PVOP_CALL()

On Wed, Oct 04, 2017 at 10:58:28AM -0500, Josh Poimboeuf wrote:
> Remove the inline asm duplication in ____PVOP_CALL().
> 
> Also add 'IS_ENABLED(CONFIG_X86_32)' to the return variable logic,
> making the code clearer and rendering the comment unnecessary.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  arch/x86/include/asm/paravirt_types.h | 36 +++++++++++++----------------------
>  1 file changed, 13 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
> index ab7aabe6b668..01f9e10983c1 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -529,29 +529,19 @@ int paravirt_disable_iospace(void);
>  		rettype __ret;						\
>  		PVOP_CALL_ARGS;						\
>  		PVOP_TEST_NULL(op);					\

Newline here...

> -		/* This is 32-bit specific, but is okay in 64-bit */	\
> -		/* since this condition will never hold */		\
> -		if (sizeof(rettype) > sizeof(unsigned long)) {		\
> -			asm volatile(pre				\
> -				     paravirt_alt(PARAVIRT_CALL)	\
> -				     post				\
> -				     : call_clbr, ASM_CALL_CONSTRAINT	\
> -				     : paravirt_type(op),		\
> -				       paravirt_clobber(clbr),		\
> -				       ##__VA_ARGS__			\
> -				     : "memory", "cc" extra_clbr);	\
> -			__ret = (rettype)((((u64)__edx) << 32) | __eax); \
> -		} else {						\
> -			asm volatile(pre				\
> -				     paravirt_alt(PARAVIRT_CALL)	\
> -				     post				\
> -				     : call_clbr, ASM_CALL_CONSTRAINT	\
> -				     : paravirt_type(op),		\
> -				       paravirt_clobber(clbr),		\
> -				       ##__VA_ARGS__			\
> -				     : "memory", "cc" extra_clbr);	\
> -			__ret = (rettype)(__eax & PVOP_RETMASK(rettype));	\
> -		}							\
> +		asm volatile(pre					\
> +			     paravirt_alt(PARAVIRT_CALL)		\
> +			     post					\
> +			     : call_clbr, ASM_CALL_CONSTRAINT		\
> +			     : paravirt_type(op),			\
> +			       paravirt_clobber(clbr),			\
> +			       ##__VA_ARGS__				\
> +			     : "memory", "cc" extra_clbr);		\

... and here goes a long way towards readability. :)

> +		if (IS_ENABLED(CONFIG_X86_32) &&			\
> +		    sizeof(rettype) > sizeof(unsigned long))		\
> +			__ret = (rettype)((((u64)__edx) << 32) | __eax);\
> +		else							\
> +			__ret = (rettype)(__eax & PVOP_RETMASK(rettype));\
>  		__ret;							\
>  	})

-- 
Regards/Gruss,
    Boris.

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