[PATCH] make KVM conform to sucky rdmsr interface

[PATCH] make KVM conform to sucky rdmsr interface

[Rusty Russell]

Grrr.... Andi refused to take my "rdmsr64" patch which moved to a
function-like interface for MSRs, dismissing it as pointless churn.

paravirt_ops cleanups changed a macro to an inline and spotted this
kvm bug.

Signed-off-by: Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>

diff -r 47c6ee74a5c5 drivers/kvm/vmx.c
--- a/drivers/kvm/vmx.c	Thu Mar 22 12:57:44 2007 +1100
+++ b/drivers/kvm/vmx.c	Thu Mar 22 13:38:24 2007 +1100
@@ -1127,7 +1127,7 @@ static int vmx_vcpu_setup(struct kvm_vcp
 		u64 data;
 		int j = vcpu->nmsrs;
 
-		if (rdmsr_safe(index, &data_low, &data_high) < 0)
+		if (rdmsr_safe(index, data_low, data_high) < 0)
 			continue;
 		if (wrmsr_safe(index, data_low, data_high) < 0)
 			continue;



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

[Avi Kivity]

Rusty Russell wrote:
> Grrr.... Andi refused to take my "rdmsr64" patch which moved to a
> function-like interface for MSRs, dismissing it as pointless churn.
>
> paravirt_ops cleanups changed a macro to an inline and spotted this
> kvm bug.
>
> Signed-off-by: Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>
>
> diff -r 47c6ee74a5c5 drivers/kvm/vmx.c
> --- a/drivers/kvm/vmx.c	Thu Mar 22 12:57:44 2007 +1100
> +++ b/drivers/kvm/vmx.c	Thu Mar 22 13:38:24 2007 +1100
> @@ -1127,7 +1127,7 @@ static int vmx_vcpu_setup(struct kvm_vcp
>  		u64 data;
>  		int j = vcpu->nmsrs;
>  
> -		if (rdmsr_safe(index, &data_low, &data_high) < 0)
> +		if (rdmsr_safe(index, data_low, data_high) < 0)
>  			continue;
>  		if (wrmsr_safe(index, data_low, data_high) < 0)
>  			continue;
>
>
>   

My rdmsr_safe (x86_64, i386 is similar/same) is

#define rdmsr_safe(msr,a,b) \
        ({ int ret__;                                           \
          asm volatile ("1:       rdmsr\n"                      \
                      "2:\n"                                    \
                      ".section .fixup,\"ax\"\n"                \
                      "3:       movl %4,%0\n"                   \
                      " jmp 2b\n"                               \
                      ".previous\n"                             \
                      ".section __ex_table,\"a\"\n"             \
                      " .align 8\n"                             \
                      " .quad 1b,3b\n"                          \
                      ".previous":"=&bDS" (ret__), "=a"(*(a)), "=d"(*(b))\
                      :"c"(msr), "i"(-EIO), "0"(0));            \
          ret__; })


Which seems quite happy to accept pointers to the values. The one in 
asm/i386/paravirt.h has a similar calling convention.


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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

[Rusty Russell]

On Thu, 2007-03-22 at 09:20 +0200, Avi Kivity wrote:
> My rdmsr_safe (x86_64, i386 is similar/same) is

Erk.  Andrew, please drop that patch, and take this one.

It was actually Jeremy's paravirt cleanup patch which changed the
calling convention of rdmsr_safe() to match rdmsr().

I went "oh it's that fucking rdmsr interface" and "fixed" kvm.

Sorry for the bad patch,
Rusty.
==
rdmsr_safe() takes pointers.  rdmsr() modifies its arguments.  What a
mess.

Fix rdmsr_safe() with !CONFIG_PARAVIRT.

Signed-off-by: Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>

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;							\
 	})
 



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

[Jeremy Fitzhardinge]

Rusty Russell wrote:
> It was actually Jeremy's paravirt cleanup patch which changed the
> calling convention of rdmsr_safe() to match rdmsr().
>   

Oops, my little mind hobgoblin is getting out of control...

    J

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

[Andrew Morton]

On Thu, 22 Mar 2007 18:49:30 +1100
Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org> wrote:

> rdmsr_safe() takes pointers.  rdmsr() modifies its arguments.  What a
> mess.
> 
> Fix rdmsr_safe() with !CONFIG_PARAVIRT.
> 
> Signed-off-by: Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>
> 
> 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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Re: [PATCH] make KVM conform to sucky rdmsr interface

[Jeremy Fitzhardinge]

Andrew Morton wrote:
> Which tree are you patching??
> -

It looks like its against the previously posted "Cleanup: rationalize
paravirt wrappers" patch.

    J

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

[Rusty Russell]

On Thu, 2007-03-22 at 14:30 -0700, Andrew Morton wrote:
> Which tree are you patching??

We crossed in the mail: you turfed out the paravirt.h cleanup patch it
applied to.

We have rolled the fixes one patch, and am testing...

Rusty.



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