linux-kernel - Re: [Xen-devel] [V2 PATCH 1/1] PVH: set EFER.NX and EFER.SCE

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Date:	Wed, 3 Sep 2014 13:53:13 -0700
From:	Mukesh Rathor <mukesh.rathor@...cle.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	<boris.ostrovsky@...cle.com>, <xen-devel@...ts.xenproject.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [V2 PATCH 1/1] PVH: set EFER.NX and EFER.SCE

On Wed, 3 Sep 2014 14:58:04 +0100
David Vrabel <david.vrabel@...rix.com> wrote:

> On 03/09/14 02:19, Mukesh Rathor wrote:
> > This patch addresses two things for a pvh boot vcpu:
> > 
> >   - NX bug on intel: It was recenlty discovered that NX is not being
> >     honored in PVH on intel since EFER.NX is not being set.
> > 
> >   - PVH boot hang on newer xen:  Following c/s on xen
> > 
> >         c/s 7645640:  x86/PVH: don't set EFER_SCE for pvh guest
> > 
> >     removes setting of EFER.SCE for PVH guests. As such, existing
> > intel pvh guest will no longer boot on xen after that c/s.
> > 
> > Both above changes will be applicable to AMD also when xen support
> > of AMD pvh is added.
> > 
> > Also, we create a new glue assembly entry point for secondary vcpus
> > because they come up on kernel page tables that have pte.NX
> > bits set. As such, before anything is touched in DS/SS, EFER.NX
> > must be set.
> [...]
> > --- a/arch/x86/xen/xen-head.S
> > +++ b/arch/x86/xen/xen-head.S
> > @@ -47,6 +47,35 @@ ENTRY(startup_xen)
> >  
> >  	__FINIT
> >  
> > +#ifdef CONFIG_XEN_PVH
> > +#ifdef CONFIG_X86_64
> > +.macro PVH_EARLY_SET_EFER
> 
> I don't think a macro is the right way to do this.  We can instead
> pass a parameter to say whether it is a boot or secondary CPU.
> 
> Something like this (untested) patch?

That's fine too. But, since vcpu 0 is always primary vcpu, we can
just use that and not worry about passing another parameter.

-Mukesh

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