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 07/07/2015 05:11 AM, Jan Beulich wrote:
>>>> On 29.06.15 at 22:21, <boris.ostrovsky@oracle.com> wrote:
>> In preparation for enabling 32-bit PVH guests replace a number of guest mode's
>> tests that assume a PV guest with has_32bit_shinfo() that can be applicable
>> to
>> both PV and PVH guests.
> Apart from this apparently needing re-basing, I also think this should
> be swapped with patch 2, as right now it doesn't make much sense to
> distinguish the two checks.
>
>> @@ -737,7 +737,7 @@ int arch_set_info_guest(
>>   
>>       /* The context is a compat-mode one if the target domain is compat-mode;
>>        * we expect the tools to DTRT even in compat-mode callers. */
>> -    compat = is_pv_32on64_domain(d);
>> +    compat = has_32bit_shinfo(d);
> Furthermore, looking at uses like this, tying such decisions to the
> shared info layout looks kind of odd. I think for documentation
> purposes we may need a differently named alias.

Yes, it does look odd, which is why I was asking in another thread about 
having another field in domain structure (well, I was asking about 
replacing has_32bit_shinfo but I think I can see now that wouldn't be 
right).

Are you suggesting a new macro, e.g.
#define is_32b_mode(d)    ((d)->arch.has_32bit_shinfo)

or would it better to add new field? Or get_mode() hvm op, similar to 
set_mode(), which can look, say, at EFER?


>
>> @@ -1721,9 +1721,7 @@ unsigned long hypercall_create_continuation(
>>           else
>>               curr->arch.hvm_vcpu.hcall_preempted = 1;
>>   
>> -        if ( is_pv_vcpu(curr) ?
>> -             !is_pv_32bit_vcpu(curr) :
>> -             curr->arch.hvm_vcpu.hcall_64bit )
>> +        if ( !has_32bit_shinfo(curr->domain) )
> This is not a valid replacement - hcall_64bit depends on the mode
> the vCPU currently is in, while has_32bit_shinfo() doesn't.

Right, and I don't think this change is needed anyway since 
hvm_do_hypercall() will set hcall_64bit for PVH guests as well (when the 
guest is in 64-bit mode)

>
>> --- a/xen/common/domctl.c
>> +++ b/xen/common/domctl.c
>> @@ -496,7 +496,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
>>               break;
>>   
>>   #ifdef CONFIG_COMPAT
>> -        if ( !is_pv_32on64_domain(d) )
>> +        if ( !has_32bit_shinfo(d) )
>>               ret = copy_from_guest(c.nat, op->u.vcpucontext.ctxt, 1);
>>           else
>>               ret = copy_from_guest(c.cmp,
>> @@ -902,7 +902,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
>>           vcpu_unpause(v);
>>   
>>   #ifdef CONFIG_COMPAT
>> -        if ( !is_pv_32on64_domain(d) )
>> +        if ( !has_32bit_shinfo(d) )
>>               ret = copy_to_guest(op->u.vcpucontext.ctxt, c.nat, 1);
>>           else
>>               ret = copy_to_guest(guest_handle_cast(op->u.vcpucontext.ctxt,
> Where is it written down what format 32-bit PVH guests' vCPU
> contexts get passed in? It would seem to me that it would be
> rather more natural for them to use the 64-bit layout. Or else
> how do you intend to suppress them being able to enter 64-bit
> mode?

So why do we use the 'else' clause for 32b PV guests when they also use 
the same vcpu_guest_context_x86_32_t in libxc/xc_dom_x86.c:vcpu_x86_32()?

-boris