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

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:
* 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 &
+        ASSERT(!(v->arch.hvm_vmx.exec_control &
+        /*
+         * Note: we run with default VM_ENTRY_LOAD_DEBUG_CTLS of
1, which means
+         * upon vmentry, the cpu reads/loads VMCS.DR7 and
+         * 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 &=
+        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 Loading Guest Control...."
      states that setting to 0 would cause the LMA to be loaded from

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
   - 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.


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