linux-kernel - Re: [Xen-devel] [V0 PATCH 1/2] AMD-PVH: set EFER.NX and EFER.SCE for the boot vcpu

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Date:	Thu, 21 Aug 2014 21:39:04 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Mukesh Rathor <mukesh.rathor@...cle.com>
Cc:	boris.ostrovsky@...cle.com, david.vrabel@...rix.com,
	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [V0 PATCH 1/2] AMD-PVH: set EFER.NX and EFER.SCE for
 the boot vcpu

On Wed, Aug 20, 2014 at 07:16:39PM -0700, Mukesh Rathor wrote:
> On AMD, NX feature must be enabled in the efer for NX to be honored in
> the pte entries, otherwise protection fault. We also set SC for
> system calls to be enabled.

How come we don't need to do that for Intel (that is set the NX bit)?
Could you include the explanation here please?


> 
> Signed-off-by: Mukesh Rathor <mukesh.rathor@...cle.com>
> ---
>  arch/x86/xen/enlighten.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index c0cb11f..4af512d 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -1499,6 +1499,17 @@ void __ref xen_pvh_secondary_vcpu_init(int cpu)
>  	xen_pvh_set_cr_flags(cpu);
>  }
>  
> +/* This is done in secondary_startup_64 for hvm guests. */
> +static void __init xen_configure_efer(void)
> +{
> +	u64 efer;
> +
> +	rdmsrl(MSR_EFER, efer);
> +	efer |= EFER_SCE;
> +	efer |= (cpuid_edx(0x80000001) & (1 << 20)) ? EFER_NX : 0;

Ahem? #defines for these magic values please?

Or could you use 'boot_cpu_has'?

> +	wrmsrl(MSR_EFER, efer);
> +}
> +
>  static void __init xen_pvh_early_guest_init(void)
>  {
>  	if (!xen_feature(XENFEAT_auto_translated_physmap))
> @@ -1508,6 +1519,7 @@ static void __init xen_pvh_early_guest_init(void)
>  		return;
>  
>  	xen_have_vector_callback = 1;
> +	xen_configure_efer();
>  	xen_pvh_set_cr_flags(0);
>  
>  #ifdef CONFIG_X86_32
> -- 
> 1.8.3.1
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@...ts.xen.org
> http://lists.xen.org/xen-devel
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