Re: [Xen-devel] [PATCH 7/6] x86/msr: Introduce msr_{set, clear}_bits() helpers

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.06.18 at 20:22, <andrew.cooper3@xxxxxxxxxx> wrote:
> --- a/xen/include/asm-x86/msr.h
> +++ b/xen/include/asm-x86/msr.h
> @@ -11,6 +11,11 @@
>  #include <asm/asm_defns.h>
>  #include <asm/cpufeature.h>
>  
> +static inline void rdmsr_split(unsigned int msr, uint32_t *lo, uint32_t *hi)
> +{
> +    asm volatile ( "rdmsr" : "=a" (*lo), "=d" (*hi) : "c" (msr) );

What's the reason for not making this ...

> +}
> +
>  #define rdmsr(msr,val1,val2) \
>       __asm__ __volatile__("rdmsr" \
>                         : "=a" (val1), "=d" (val2) \

... use this and ...

> @@ -23,6 +28,11 @@
>         val = a__ | ((u64)b__<<32); \
>  } while(0)
>  
> +static inline void wrmsr_split(unsigned int msr, uint32_t lo, uint32_t hi)
> +{
> +    asm volatile ( "wrmsr" :: "a" (lo), "d" (hi), "c" (msr) );

... this use ... 

> +}
> +
>  #define wrmsr(msr,val1,val2) \
>       __asm__ __volatile__("wrmsr" \
>                         : /* no outputs */ \

... this? In fact it's not really clear why we need the inline functions _and_
the macros. Afaict the two new functions below could also be implemented
with just the macros.

Jan



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