Re: [PATCH 1/3] x86: drop is_pv_32on64_vcpu()

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

On 06/24/2015 07:49 PM, Andrew Cooper wrote:
> On 24/06/2015 22:35, Boris Ostrovsky wrote:
>> On 06/23/2015 11:18 AM, Jan Beulich wrote:
>>> ... as being identical to is_pv_32bit_vcpu() after the x86-32 removal.
>>>
>>> In a few cases this includes an additional is_pv_32bit_vcpu() ->
>>> is_pv_32bit_domain() conversion.
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> We have
>> struct arch_domain
>> {
>>      ...
>>      /* Is a 32-bit PV (non-HVM) guest? */
>>      bool_t is_32bit_pv;
>>      /* Is shared-info page in 32-bit format? */
>>      bool_t has_32bit_shinfo;
>>     ...
>> }
>>
>> and currently both of these fields are set/unset together (except for
>> one HVM case --- hvm_latch_shinfo_size()). Why not have a single 'bool
>> is_32bit' and then replace macros at the top of
>> include/asm-x86/domain.h with is_32bit_vcpu/domain()?
>>
>> I think in majority of places when we test for
>> is_pv_32bit_vcpu/domain() we already know that we are PV so it
>> shouldn't add any additional tests.
> For the PV case, the two are equivalent.  For HVM, they are not.
>
> HVM domains have shared info, but may be latched as either 32 or 64bit,
> depending on the mode they were running in when they most recently wrote
> a hypercall page.  Sadly, the shared info layout is width-dependent
> which is why such hacks need to exist.

Why can't we latch the mode into is_32bit field? I am essentially 
suggesting to drop is_32bit_pv and rename has_32bit_shinfo to is_32bit. 
Then is_pv_32bit_vcpu() becomes '(is_pv_vcpu() && domain->is_32bit)' (or 
simply domain->is_32bit, depending on context) and has_32bit_shinfo()  
becomes domain->is_32bit.

The reason I am asking is because for the 32b PVH I will need to switch 
a few places from using is_pv_32bit_vcpu() to has_32bit_shinfo() and 
that would look strange: asking whether the guest is 32-bit looks more 
natural than asking whether its shared info is 32-bit. At least it's 
more natural to my eye.

-boris