linux-kernel - Re: [PATCH] make KVM conform to sucky rdmsr interface

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Date:	Thu, 22 Mar 2007 14:30:11 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Avi Kivity <avi@...ranet.com>, Andi Kleen <ak@....de>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kvm-devel <kvm-devel@...ts.sourceforge.net>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH] make KVM conform to sucky rdmsr interface

On Thu, 22 Mar 2007 18:49:30 +1100
Rusty Russell <rusty@...tcorp.com.au> wrote:

> rdmsr_safe() takes pointers.  rdmsr() modifies its arguments.  What a
> mess.
> 
> Fix rdmsr_safe() with !CONFIG_PARAVIRT.
> 
> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
> 
> diff -r a7f78e8eacc8 include/asm-i386/msr.h
> --- a/include/asm-i386/msr.h	Thu Mar 22 12:38:35 2007 +1100
> +++ b/include/asm-i386/msr.h	Thu Mar 22 18:40:35 2007 +1100
> @@ -96,12 +96,12 @@ static inline void wrmsrl (unsigned long
>  	(native_write_msr(msr, ((unsigned long long)val2 << 32) | val1))
>  
>  /* rdmsr with exception handling */
> -#define rdmsr_safe(msr,val1,val2)						\
> +#define rdmsr_safe(msr,p1,p2)						\
>  	({								\
>  		int __err;						\
> -		unsigned long long __val = native_read_msr(msr, &__err);	\
> -		val1 = __val;						\
> -		val2 = __val >> 32;					\
> +		unsigned long long __val = native_read_msr(msr, &__err);\
> +		(*p1) = __val;						\
> +		(*p2) = __val >> 32;					\
>  		__err;							\
>  	})


Linus's tree has

/* rdmsr with exception handling */
#define rdmsr_safe(msr,a,b) ({ int ret__;						\
	asm volatile("2: rdmsr ; xorl %0,%0\n"						\
		     "1:\n\t"								\
		     ".section .fixup,\"ax\"\n\t"					\
		     "3:  movl %4,%0 ; jmp 1b\n\t"					\
		     ".previous\n\t"							\
 		     ".section __ex_table,\"a\"\n"					\
		     "   .align 4\n\t"							\
		     "   .long 	2b,3b\n\t"						\
		     ".previous"							\
		     : "=r" (ret__), "=a" (*(a)), "=d" (*(b))				\
		     : "c" (msr), "i" (-EFAULT));\
	ret__; })

(secret decoder ring: resize your xterm to 100 cols to read the above.  Sigh).

Which tree are you patching??
-
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