Re: [PATCH 1/5] x86: introduce read_sregs() to allow storing to memory directly

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 28/09/2020 13:05, Jan Beulich wrote:
> --- a/xen/include/asm-x86/regs.h
> +++ b/xen/include/asm-x86/regs.h
> @@ -15,4 +15,18 @@
>      (diff == 0);                                                             
>  \
>  })
>  
> +#define read_sreg(name) ({                                    \
> +    unsigned int __sel;                                       \
> +    asm volatile ( "mov %%" STR(name) ",%0" : "=r" (__sel) ); \
> +    __sel;                                                    \
> +})
> +
> +static inline void read_sregs(struct cpu_user_regs *regs)
> +{
> +    asm volatile ( "mov %%ds, %0" : "=m" (regs->ds) );
> +    asm volatile ( "mov %%es, %0" : "=m" (regs->es) );
> +    asm volatile ( "mov %%fs, %0" : "=m" (regs->fs) );
> +    asm volatile ( "mov %%gs, %0" : "=m" (regs->gs) );

It occurs to me that reads don't need to be volatile.  There are no side
effects.

With that fixed, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>