Re: [Xen-devel] [PATCH 18/18] PVH xen: introduce vmx_pvh.c

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Tue, 25 Jun 2013 11:49:57 +0100
"Jan Beulich" <JBeulich@xxxxxxxx> wrote:
.......

> > +int vmx_pvh_set_vcpu_info(struct vcpu *v, struct
> > vcpu_guest_context *ctxtp) +{
> > +    if ( v->vcpu_id == 0 )
> > +        return 0;
> > +
> > +    vmx_vmcs_enter(v);
> > +    __vmwrite(GUEST_GDTR_BASE, ctxtp->gdt.pvh.addr);
> > +    __vmwrite(GUEST_GDTR_LIMIT, ctxtp->gdt.pvh.limit);
> > +    __vmwrite(GUEST_GS_BASE, ctxtp->gs_base_user);
> > +
> > +    __vmwrite(GUEST_CS_SELECTOR, ctxtp->user_regs.cs);
> > +    __vmwrite(GUEST_DS_SELECTOR, ctxtp->user_regs.ds);
> > +    __vmwrite(GUEST_ES_SELECTOR, ctxtp->user_regs.es);
> > +    __vmwrite(GUEST_SS_SELECTOR, ctxtp->user_regs.ss);
> > +    __vmwrite(GUEST_GS_SELECTOR, ctxtp->user_regs.gs);
> 
> How does this work without also writing the "hidden" register
> fields?

This is for bringing up SMP CPUs by the guest, which already has set GDT
up so it just needs selectors to be loaded to start the target vcpu.

> > +    if ( vmx_add_guest_msr(MSR_SHADOW_GS_BASE) )
> > +    {
> > +        vmx_vmcs_exit(v);
> > +        return -EINVAL;
> > +    }
> > +    vmx_write_guest_msr(MSR_SHADOW_GS_BASE, ctxtp->gs_base_kernel);
> 
> So you write both GS bases, but not the base of FS (and above
> its selector is being skipped too)?

Right, for 32bit PVH we'd need to do that. It needs PVH 32bitfixme tag.
Or I can just do it for both, 64bit would be null anyways.

> And there are other parts of struct vcpu_guest_context that
> I don't see getting mirrored - are all of them getting handled
> elsewhere?

The call comes from VCPUOP_initialise -> arch_set_info_guest() which handles 
some of the other fields. There's lot less to load for PVH compared to
PV.

thanks
mukesh


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