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 10:30 AM, Boris Ostrovsky wrote:
> 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.

Forgot to include here --- so what is your preference wrt what I am 
asking in the first paragraph? d->vcpu[0], new field (or maybe a flag 
with bits per 32bit-pv and 32bit-pvh), or a PVH-wrapper for 
has_32bit_shinfo?

-boris

-boris