Re: [Xen-devel] [V10 PATCH 21/23] PVH xen: VMX support of PVH guest creation/destruction

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Fri, 9 Aug 2013 14:44:48 +0100
George Dunlap <dunlapg@xxxxxxxxx> wrote:

> On Wed, Jul 24, 2013 at 2:59 AM, Mukesh Rathor
> <mukesh.rathor@xxxxxxxxxx> wrote:
> > This patch implements the vmx portion of the guest create, ie
> > vcpu and domain initialization. Some changes to support the destroy
> > path.
> >
> > Change in V10:
> >   - Don't call vmx_domain_initialise / vmx_domain_destroy for PVH.
> >   - Do not set hvm_vcpu.guest_efer here in vmx.c.
> >
> > Signed-off-by: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
> > ---
> >  xen/arch/x86/hvm/vmx/vmx.c |   28 ++++++++++++++++++++++++++++
> >  1 files changed, 28 insertions(+), 0 deletions(-)
> >
> > diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> > index 80109c1..f6ea39a 100644
> > --- a/xen/arch/x86/hvm/vmx/vmx.c
> > +++ b/xen/arch/x86/hvm/vmx/vmx.c
> > @@ -1076,6 +1076,28 @@ static void vmx_update_host_cr3(struct vcpu
> > *v) vmx_vmcs_exit(v);
> >  }
> >
> > +/*
> > + * PVH guest never causes CR3 write vmexit. This is called during
> > the guest
> > + * setup.
> > + */
> > +static void vmx_update_pvh_cr(struct vcpu *v, unsigned int cr)
> > +{
> > +    vmx_vmcs_enter(v);
> > +    switch ( cr )
> > +    {
> > +    case 3:
> > +        __vmwrite(GUEST_CR3, v->arch.hvm_vcpu.guest_cr[3]);
> > +        hvm_asid_flush_vcpu(v);
> > +        break;
> > +
> > +    default:
> > +        printk(XENLOG_ERR
> > +               "PVH: d%d v%d unexpected cr%d update at rip:%lx\n",
> > +               v->domain->domain_id, v->vcpu_id, cr,
> > __vmread(GUEST_RIP));
> > +    }
> > +    vmx_vmcs_exit(v);
> > +}
> 
> This function seems almost completely pointless.  In the case of CR3,
> it basically does exactly what the function below does.  It avoids
> maybe doing something pointless, like vmx_load_ptrs(), but that should
> be harmless, right?

Harmless, nonetheless pointless paying small penalty calling it. Such
things are subjective and matter of personal opinions, and vary from
maintainer to maintainer.... I don't care either way. If it helps this
patch end it's misery, I'll make the change!

Mukesh


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