From mboxrd@z Thu Jan  1 00:00:00 1970
From: George Dunlap <george.dunlap@eu.citrix.com>
Subject: Re: [PATCH RFC v12 08/21] pvh: vmx-specific changes
Date: Tue, 17 Sep 2013 09:48:08 +0100
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To: Mukesh Rathor <mukesh.rathor@oracle.com>
Cc: Keir Fraser <keir@xen.org>, Tim Deegan <tim@xen.org>, Jan Beulich <jan.beulich@suse.com>, xen-devel@lists.xen.org
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On 09/17/2013 12:12 AM, Mukesh Rathor wrote:
> On Fri, 13 Sep 2013 17:38:41 +0100
> George Dunlap <george.dunlap@eu.citrix.com> 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