Re: [Xen-devel] [PATCH RFC v12 08/21] pvh: vmx-specific changes

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 09/17/2013 12:12 AM, Mukesh Rathor wrote:
> On Fri, 13 Sep 2013 17:38:41 +0100
> George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
>
> > On 13/09/13 17:25, George Dunlap wrote:
> > > Changes:
> > > * Enforce HAP mode for now
> > > * Disable exits related to virtual interrupts or emulated APICs
> > > * Disable changing paging mode
> > >    - "unrestricted guest" (i.e., real mode for EPT) disabled
> ........
> > > +        ASSERT(v->arch.hvm_vmx.exec_control &
> > > CPU_BASED_ACTIVATE_MSR_BITMAP);
> > > +        ASSERT(!(v->arch.hvm_vmx.exec_control &
> > > CPU_BASED_RDTSC_EXITING)); +
> > > +        /*
> > > +         * Note: we run with default VM_ENTRY_LOAD_DEBUG_CTLS of
> > > 1, which means
> > > +         * upon vmentry, the cpu reads/loads VMCS.DR7 and
> > > VMCS.DEBUGCTLS, and not
> > > +         * use the host values. 0 would cause it to not use the
> > > VMCS values.
> > > +         */
> > > +
> > > +        /* PVH: I don't think these are necessary */
> > > +        v->arch.hvm_vmx.exec_control &=
> > > ~CPU_BASED_VIRTUAL_NMI_PENDING;
> > > +        vmentry_ctl &= ~VM_ENTRY_LOAD_GUEST_EFER;
> > > +        vmentry_ctl &= ~VM_ENTRY_SMM;
> > > +        vmentry_ctl &= ~VM_ENTRY_DEACT_DUAL_MONITOR;
> > Mukesh, I couldn't figure out why you had set these.  What are these
> > about, and are they really necessary?
> We clear those because:
>    - VM_ENTRY_LOAD_GUEST_EFER: "Intel sdm 23.3.2.1 Loading Guest Control...."
>       states that setting to 0 would cause the LMA to be loaded from
>       VM_ENTRY_IA32E_MODE.
OK -- but if we just set the LMA properly in the vmcs or wherever, and 
prevent the guest from changing it, then it will DTRT, won't it?
>    - VM_ENTRY_SMM: also according to the SDM must be 0 if not entering from
>                     SMM.
>    - VM_ENTRY_DEACT_DUAL_MONITOR: same, must be 0 for entry outside SMM.
But those have nothing to do with PVH -- Plain HVM guests needs that as 
well.  So they're already being cleared (or never being set) -- we don't 
need to add these lines in a PVH-specific section.
 -George

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