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Re: [Xen-devel] [PATCH 1/4] x86: remove CR reads from exit-to-guest path

On 23/01/18 10:36, Jan Beulich wrote:
> --- a/xen/include/asm-x86/asm_defns.h
> +++ b/xen/include/asm-x86/asm_defns.h
> @@ -206,13 +206,12 @@ void ret_from_intr(void);
>  #define ASM_STAC ASM_AC(STAC)
>  #define ASM_CLAC ASM_AC(CLAC)
> -.macro write_cr3 val:req, tmp1:req, tmp2:req
> -        mov   %cr4, %\tmp1
> -        mov   %\tmp1, %\tmp2
> -        and   $~X86_CR4_PGE, %\tmp1
> -        mov   %\tmp1, %cr4
> +.macro write_cr3 val:req, cr4:req, tmp:req
> +        mov   %\cr4, %\tmp
> +        and   $~X86_CR4_PGE, %\cr4
> +        mov   %\cr4, %cr4

This is confusing to read; It took me a while to work out why it
assembled in the first place.  Given that there are only two instances
of write_cr3 now, I'd suggest expanding this in the two sites.  It will
also make it clear which registers have real values and which are
temporary, which isn't clear from the current callsites.

Otherwise, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

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