Re: [PATCH v2 1/4] x86/compat: Test whether guest has 32b shinfo instead of being a PV 32b domain

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 07/09/2015 10:17 AM, Jan Beulich wrote:
>>>> On 09.07.15 at 16:10, <boris.ostrovsky@oracle.com> wrote:
>> On 07/09/2015 03:02 AM, Jan Beulich wrote:
>>>>>> On 08.07.15 at 22:57, <boris.ostrovsky@oracle.com> wrote:
>>>> As I started to update the patches I realized that in some cases
>>>> (especially in arch_do_domctl():XEN_DOMCTL_get_address_size) we don't
>>>> have VCPU (which is what hvm_guest_x86_mode() wants) but rather only the
>>>> domain. d->vcpu[0] should work. Otherwise I'll either need a new field
>>>> in struct domain or wrap has_32bit_shinfo into something PVH-specific,
>>>> like is_32bit_pvh_vcpu().
>>> Shouldn't XEN_DOMCTL_get_address_size be handled HVM-like
>>> for PVH, especially if you also intend the tools to use the 64-bit
>>> guest context variant even for 32-bit PVH? Once again - are you
>>> intending to prohibit 32-bit PVH switching to 64-bit mode (which
>>> would seem both wrong and possibly cumbersome to me)?
>> With current PVH implementation I don't think we can switch. We are
>> starting the guest in very much PV-like fashion. That's why we are
>> getting into switch_compat() --- via XEN_DOMCTL_set_address_size.
>>
>> For XEN_DOMCTL_get_address_size specifically we need to be able to
>> figure out the mode *before* the guest is running because we use it to
>> set cpuid bits in xc_cpuid_pv_policy(). So just that means we can't
>> change the mode.
> Okay - but is there code (being put) in place to refuse switch
> attempts?

No, I should add code to deal with this.


-boris