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Date:   Wed, 6 May 2020 17:18:01 -0500
From:   Segher Boessenkool <segher@kernel.crashing.org>
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
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        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v4 1/2] powerpc/uaccess: Implement unsafe_put_user() using 'asm goto'
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References: <23e680624680a9a5405f4b88740d2596d4b17c26.1587143308.git.christophe.leroy@c-s.fr> <87sggecv81.fsf@mpe.ellerman.id.au> <20200505153245.GN31009@gate.crashing.org> <87pnbhdgkw.fsf@mpe.ellerman.id.au> <20200506175849.GT31009@gate.crashing.org> <bd336b0f-9cf7-e2ce-e0a8-1891599638d1@csgroup.eu>
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On Wed, May 06, 2020 at 08:10:57PM +0200, Christophe Leroy wrote:
> Le 06/05/2020 à 19:58, Segher Boessenkool a écrit :
> >>  #define __put_user_asm_goto(x, addr, label, op)			\
> >>  	asm volatile goto(					\
> >>-		"1:	" op "%U1%X1 %0,%1	# put_user\n"	\
> >>+		"1:	" op "%X1 %0,%1	# put_user\n"		\
> >>  		EX_TABLE(1b, %l2)				\
> >>  		:						\
> >>-		: "r" (x), "m<>" (*addr)				\
> >>+		: "r" (x), "m" (*addr)				\
> >>  		:						\
> >>  		: label)
> >
> >Like that.  But you will have to do that to *all* places we use the "<>"
> >constraints, or wait for more stuff to fail?  And, there probably are
> >places we *do* want update form insns used (they do help in some loops,
> >for example)?
> >
> 
> AFAICT, git grep "m<>" provides no result.

Ah, okay.

> However many places have %Ux:

<snip>

Yes, all of those are from when "m" still meant what "m<>" is now.  For
seeing how many update form insns can be generated (and how much that
matters), these all should be fixed, at a minimum.


Segher

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Date: Wed, 6 May 2020 17:18:01 -0500
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Subject: Re: [PATCH v4 1/2] powerpc/uaccess: Implement unsafe_put_user() using
 'asm goto'
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References: <23e680624680a9a5405f4b88740d2596d4b17c26.1587143308.git.christophe.leroy@c-s.fr>
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On Wed, May 06, 2020 at 08:10:57PM +0200, Christophe Leroy wrote:
> Le 06/05/2020 à 19:58, Segher Boessenkool a écrit :
> >>  #define __put_user_asm_goto(x, addr, label, op)			\
> >>  	asm volatile goto(					\
> >>-		"1:	" op "%U1%X1 %0,%1	# put_user\n"	\
> >>+		"1:	" op "%X1 %0,%1	# put_user\n"		\
> >>  		EX_TABLE(1b, %l2)				\
> >>  		:						\
> >>-		: "r" (x), "m<>" (*addr)				\
> >>+		: "r" (x), "m" (*addr)				\
> >>  		:						\
> >>  		: label)
> >
> >Like that.  But you will have to do that to *all* places we use the "<>"
> >constraints, or wait for more stuff to fail?  And, there probably are
> >places we *do* want update form insns used (they do help in some loops,
> >for example)?
> >
> 
> AFAICT, git grep "m<>" provides no result.

Ah, okay.

> However many places have %Ux:

<snip>

Yes, all of those are from when "m" still meant what "m<>" is now.  For
seeing how many update form insns can be generated (and how much that
matters), these all should be fixed, at a minimum.


Segher