linux-kernel - Re: [PATCH 2/2] arm:kvm remove len 8 for mmio read write buf

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Date:	Mon, 22 Dec 2014 11:51:27 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Peng Fan <van.freenix@...il.com>,
	"christoffer.dall@...aro.org" <christoffer.dall@...aro.org>
CC:	"gleb@...nel.org" <gleb@...nel.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] arm:kvm remove len 8 for mmio read write buf

On 22/12/14 11:23, Peng Fan wrote:
> For arm 32 bit architecture, 8 bytes load/store operation in one instruction
> will not be generated by compiler.

Ever heard of lrdr/strd?

> And before invoke mmio_read_buf, there is a piece of code:
> "
>                  len = run->mmio.len;
>                  if (len > sizeof(unsigned long))
>                          return -EINVAL;
> 
> 		data = mmio_read_buf(run->mmio.data, len);
> "
> 
> This piece code also tells that len variable does not exceeds 4 bytes.
> So, remove 8 bytes assign in mmio_read_buf and mmio_write_buf.

NAK. This code is shared between arm and arm64. See commit f42798c.

	M.

> 
> Signed-off-by: Peng Fan <van.freenix@...il.com>
> CC: Gleb Natapov <gleb@...nel.org>
> CC: Paolo Bonzini <pbonzini@...hat.com>
> CC: Christoffer Dall <christoffer.dall@...aro.org>
> CC: Marc Zyngier <marc.zyngier@....com>
> CC: Russell King <linux@....linux.org.uk>
> ---
>  arch/arm/kvm/mmio.c | 10 ----------
>  1 file changed, 10 deletions(-)
> 
> diff --git a/arch/arm/kvm/mmio.c b/arch/arm/kvm/mmio.c
> index 4cb5a93..953a819 100644
> --- a/arch/arm/kvm/mmio.c
> +++ b/arch/arm/kvm/mmio.c
> @@ -30,7 +30,6 @@ static void mmio_write_buf(char *buf, unsigned int len, unsigned long data)
>  		u8	byte;
>  		u16	hword;
>  		u32	word;
> -		u64	dword;
>  	} tmp;
>  
>  	switch (len) {
> @@ -46,10 +45,6 @@ static void mmio_write_buf(char *buf, unsigned int len, unsigned long data)
>  		tmp.word	= data;
>  		datap		= &tmp.word;
>  		break;
> -	case 8:
> -		tmp.dword	= data;
> -		datap		= &tmp.dword;
> -		break;
>  	}
>  
>  	memcpy(buf, datap, len);
> @@ -61,7 +56,6 @@ static unsigned long mmio_read_buf(char *buf, unsigned int len)
>  	union {
>  		u16	hword;
>  		u32	word;
> -		u64	dword;
>  	} tmp;
>  
>  	switch (len) {
> @@ -76,10 +70,6 @@ static unsigned long mmio_read_buf(char *buf, unsigned int len)
>  		memcpy(&tmp.word, buf, len);
>  		data = tmp.word;
>  		break;
> -	case 8:
> -		memcpy(&tmp.dword, buf, len);
> -		data = tmp.dword;
> -		break;
>  	}
>  
>  	return data;
> 


-- 
Jazz is not dead. It just smells funny...
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