[Xen-devel] Re: [PATCH 05/13] Nested Virtualization: CRn & paged real mode

[Christoph Egger <Christoph.Egger@xxxxxxx>]

On Wednesday 08 September 2010 17:11:33 Tim Deegan wrote:
> Hi,
>
> > diff -r 0199b689a2d0 -r e0eae5b67977 xen/arch/x86/hvm/hvm.c
> > --- a/xen/arch/x86/hvm/hvm.c
> > +++ b/xen/arch/x86/hvm/hvm.c
> > @@ -54,6 +54,7 @@
> >  #include <asm/hvm/support.h>
> >  #include <asm/hvm/cacheattr.h>
> >  #include <asm/hvm/trace.h>
> > +#include <asm/hvm/nestedhvm.h>
> >  #include <asm/mtrr.h>
> >  #include <asm/apic.h>
> >  #include <public/sched.h>
> > @@ -1109,9 +1110,13 @@ int hvm_set_cr0(unsigned long value)
> >      /* ET is reserved and should be always be 1. */
> >      value |= X86_CR0_ET;
> >
> > -    if ( (value & (X86_CR0_PE | X86_CR0_PG)) == X86_CR0_PG )
> > +    if ( !nestedhvm_vmentry_emulate(v) &&
> > +         (value & (X86_CR0_PE | X86_CR0_PG)) == X86_CR0_PG )
> >          goto gpf;
>
> The change above makes perfect sense: nested SVM guests should be
> allowed to enter paged real mode.
>
> But I don't understand either of the changes below.  Can you explain why
> the cache control bits get special treatment?

Your question confuses me related to this mail:
http://lists.xensource.com/archives/html/xen-devel/2010-08/msg00432.html

Please explain what you want to know.

Christoph


> Tim.
>
> > +    if ( nestedhvm_vcpu_in_guestmode(v) )
> > +        value &= ~(X86_CR0_CD | X86_CR0_NW);
> > +
> >      if ( (value & X86_CR0_PG) && !(old_value & X86_CR0_PG) )
> >      {
> >          if ( v->arch.hvm_vcpu.guest_efer & EFER_LME )
> > @@ -1163,7 +1168,7 @@ int hvm_set_cr0(unsigned long value)
> >          }
> >      }
> >
> > -    if ( has_arch_mmios(v->domain) )
> > +    if ( !nestedhvm_vmentry_emulate(v) && has_arch_mmios(v->domain) )
> >      {
> >          if ( (value & X86_CR0_CD) && !(value & X86_CR0_NW) )
> >          {



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