Re: [Xen-devel] [PATCH] reenabling ptrace for paravirtualized guests

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 12 May 2006, at 08:07, Simon Kagstrom wrote:

> >         ctxt.gs_base_kernel = (unsigned long)(cpu_pda(vcpu));
> >  #endif
> > +   /* set sane cr0 bits, protected and paging enabled  */
> > +   ctxt.ctrlreg[0] = 0x80000001;
> >
> >         BUG_ON(HYPERVISOR_vcpu_op(VCPUOP_initialise, vcpu, &ctxt));
> >  }
> I'll add this to the patch.
This can be done entirely in Xen without guest modification and 
avoiding magic numbers.
Add the following to arch_set_info_guest, immediately after the memcpy 
to guest_context:
  /* Only CR0.TS is modifiable by guest or admin. */
  v->arch.guest_context.ctrl_reg[0] &= X86_CR0_TS;
  v->arch.guest_context.ctrl_reg[0] |= read_cr0() & ~X86_CR0_TS;

Whether we should fill in from real CR0 or simply set a static 
selection of flags is open to debate. I don't really think it matters 
either way.
 -- Keir


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