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From: "H. Peter Anvin" <hpa@zytor.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: kernel-janitors@lists.osdl.org, kexec@lists.infradead.org,
	Shani Moideen <shani.moideen@wipro.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [KJ PATCH] Replacing memcpy(dest, src, PAGE_SIZE) with copy_page(dest, src) in arch/i386/kernel/machine_kexec.c
Date: Tue, 12 Jun 2007 09:52:07 -0700	[thread overview]
Message-ID: <466ECF37.6040303@zytor.com> (raw)
In-Reply-To: <m1vedtpwks.fsf@ebiederm.dsl.xmission.com>

Eric W. Biederman wrote:
> Shani Moideen <shani.moideen@wipro.com> writes:
> 
>> Hi,
>> Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) in
>> arch/i386/kernel/machine_kexec.c.
> 
> Please no.
> 
> People get creative in copy_page (especially mmx_copy_page),
> and this code path need something simple and stupid, that
> will work every time, especially when things are messed up
> elsewhere.
> 

memcpy() is pretty creative, too.  If you want something really dumb and
robust, you should probably create an inline:

/*
 * Eric sez: his code path need something simple and stupid, that
 * will work every time, especially when things are messed up
 * elsewhere.
 */
static inline void braindead_copy_page(void *dst, void *src)
{
	unsigned long ctr = PAGE_SIZE >> 2;

	asm volatile("cld; rep; movsl"
			: "+D" (dst), "+S" (src), "+c" (ctr)
			: : "memory");
}

(FWIW, the "cld" is supposed to be redundant, as DF=0 is supposed to be
guaranteed by the ABI.)

	-hpa

_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

WARNING: multiple messages have this Message-ID (diff)
From: "H. Peter Anvin" <hpa@zytor.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Shani Moideen <shani.moideen@wipro.com>,
	kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
	kernel-janitors@lists.osdl.org
Subject: [KJ] Re: [KJ PATCH] Replacing memcpy(dest, src,
Date: Tue, 12 Jun 2007 16:52:07 +0000	[thread overview]
Message-ID: <466ECF37.6040303@zytor.com> (raw)
In-Reply-To: <m1vedtpwks.fsf@ebiederm.dsl.xmission.com>

Eric W. Biederman wrote:
> Shani Moideen <shani.moideen@wipro.com> writes:
> 
>> Hi,
>> Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) in
>> arch/i386/kernel/machine_kexec.c.
> 
> Please no.
> 
> People get creative in copy_page (especially mmx_copy_page),
> and this code path need something simple and stupid, that
> will work every time, especially when things are messed up
> elsewhere.
> 

memcpy() is pretty creative, too.  If you want something really dumb and
robust, you should probably create an inline:

/*
 * Eric sez: his code path need something simple and stupid, that
 * will work every time, especially when things are messed up
 * elsewhere.
 */
static inline void braindead_copy_page(void *dst, void *src)
{
	unsigned long ctr = PAGE_SIZE >> 2;

	asm volatile("cld; rep; movsl"
			: "+D" (dst), "+S" (src), "+c" (ctr)
			: : "memory");
}

(FWIW, the "cld" is supposed to be redundant, as DF=0 is supposed to be
guaranteed by the ABI.)

	-hpa
_______________________________________________
Kernel-janitors mailing list
Kernel-janitors@lists.linux-foundation.org
https://lists.linux-foundation.org/mailman/listinfo/kernel-janitors

WARNING: multiple messages have this Message-ID (diff)
From: "H. Peter Anvin" <hpa@zytor.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Shani Moideen <shani.moideen@wipro.com>,
	kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
	kernel-janitors@lists.osdl.org
Subject: Re: [KJ PATCH] Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) in arch/i386/kernel/machine_kexec.c
Date: Tue, 12 Jun 2007 09:52:07 -0700	[thread overview]
Message-ID: <466ECF37.6040303@zytor.com> (raw)
In-Reply-To: <m1vedtpwks.fsf@ebiederm.dsl.xmission.com>

Eric W. Biederman wrote:
> Shani Moideen <shani.moideen@wipro.com> writes:
> 
>> Hi,
>> Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) in
>> arch/i386/kernel/machine_kexec.c.
> 
> Please no.
> 
> People get creative in copy_page (especially mmx_copy_page),
> and this code path need something simple and stupid, that
> will work every time, especially when things are messed up
> elsewhere.
> 

memcpy() is pretty creative, too.  If you want something really dumb and
robust, you should probably create an inline:

/*
 * Eric sez: his code path need something simple and stupid, that
 * will work every time, especially when things are messed up
 * elsewhere.
 */
static inline void braindead_copy_page(void *dst, void *src)
{
	unsigned long ctr = PAGE_SIZE >> 2;

	asm volatile("cld; rep; movsl"
			: "+D" (dst), "+S" (src), "+c" (ctr)
			: : "memory");
}

(FWIW, the "cld" is supposed to be redundant, as DF=0 is supposed to be
guaranteed by the ABI.)

	-hpa

  reply	other threads:[~2007-06-12 16:56 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-06-12  2:45 [KJ PATCH] Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) in arch/i386/kernel/machine_kexec.c Shani Moideen
2007-06-12  2:57 ` [KJ] [KJ PATCH] Replacing memcpy(dest,src,PAGE_SIZE) with Shani Moideen
2007-06-12  2:45 ` [KJ PATCH] Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) in arch/i386/kernel/machine_kexec.c Shani Moideen
2007-06-12  5:32 ` [KJ PATCH] Replacing memcpy(dest, src, PAGE_SIZE) with copy_page(dest, src) " Eric W. Biederman
2007-06-12  5:32   ` [KJ PATCH] Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) " Eric W. Biederman
2007-06-12  5:32   ` [KJ] Re: [KJ PATCH] Replacing memcpy(dest, src, Eric W. Biederman
2007-06-12 16:52   ` H. Peter Anvin [this message]
2007-06-12 16:52     ` [KJ PATCH] Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) in arch/i386/kernel/machine_kexec.c H. Peter Anvin
2007-06-12 16:52     ` [KJ] Re: [KJ PATCH] Replacing memcpy(dest, src, H. Peter Anvin
2007-06-13 19:46     ` [KJ PATCH] Replacing memcpy(dest, src, PAGE_SIZE) with copy_page(dest, src) in arch/i386/kernel/machine_kexec.c Pavel Machek
2007-06-13 19:46       ` [KJ PATCH] Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) " Pavel Machek
2007-06-13 19:46       ` [KJ] Re: [KJ PATCH] Replacing memcpy(dest, src, Pavel Machek
  -- strict thread matches above, loose matches on Subject: below --
2007-06-12  3:16 [KJ PATCH] Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) in arch/i386/mm/init.c Shani Moideen
2007-06-12  3:28 ` [KJ] [KJ PATCH] Replacing memcpy(dest,src,PAGE_SIZE) with Shani Moideen
2007-06-12  3:16 ` [KJ PATCH] Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) in arch/i386/mm/init.c Shani Moideen
2007-06-13 19:47 ` [KJ] Re: [KJ PATCH] Replacing memcpy(dest, src, Pavel Machek
2007-06-13 19:47   ` [KJ PATCH] Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) in arch/i386/mm/init.c Pavel Machek
2007-06-13 19:47   ` Pavel Machek

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