Re: [Xen-devel] [PATCH 1/2] x86/xen: Set EFER.NX and EFER.SCE in PVH guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.09.14 at 16:11, <david.vrabel@xxxxxxxxxx> wrote:
> --- a/arch/x86/xen/xen-head.S
> +++ b/arch/x86/xen/xen-head.S
> @@ -47,6 +47,36 @@ ENTRY(startup_xen)
>  
>       __FINIT
>  
> +#ifdef CONFIG_XEN_PVH
> +
> +/**
> + * xen_pvh_cpu_early_init() - early PVH VCPU initialization
> + * @cpu: this cpu number (%rdi)
> + *
> + * Note: This is called as a function on the boot CPU and as the secondary
> + * CPU entry point.
> + */
> +ENTRY(xen_pvh_cpu_early_init)
> +     /* Gather features to see if NX implemented. */
> +     mov     $0x80000001, %eax
> +     cpuid
> +     mov     %edx,%esi
> +
> +     mov     $MSR_EFER, %ecx
> +     rdmsr
> +     bts     $_EFER_SCE, %eax
> +
> +     bt      $20,%esi
> +     jnc     1f      /* No NX, skip setting it */
> +     bts     $_EFER_NX, %eax
> +1:   wrmsr
> +
> +     cmp     $0,%rdi /* non-zero => secondary cpu */

Isn't Linux is specifically moving away from this assumption?

> +     jne     cpu_bringup_and_idle
> +     ret
> +
> +#endif /* CONFIG_XEN_PVH */

Also, does all this really need to be done in assembly?

Jan


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