Re: [RFC PATCH] xen: Introduce arch specific field to XEN_SYSCTL_physinfo

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.08.2021 22:28, Oleksandr wrote:
> On 16.08.21 10:33, Jan Beulich wrote:
>> On 14.08.2021 01:28, Oleksandr Tyshchenko wrote:
>>> --- a/xen/include/public/arch-arm.h
>>> +++ b/xen/include/public/arch-arm.h
>>> @@ -332,6 +332,11 @@ struct xen_arch_domainconfig {
>>>        */
>>>       uint32_t clock_frequency;
>>>   };
>>> +
>>> +struct arch_physinfo {
>>> +    /* Holds the bit size of IPAs in p2m tables. */
>>> +    uint32_t p2m_ipa_bits;
>>> +};
>>>   #endif /* __XEN__ || __XEN_TOOLS__ */
>>>   
>>>   struct arch_vcpu_info {
>>> --- a/xen/include/public/arch-x86/xen.h
>>> +++ b/xen/include/public/arch-x86/xen.h
>>> @@ -346,6 +346,8 @@ typedef struct xen_msr_entry {
>>>   } xen_msr_entry_t;
>>>   DEFINE_XEN_GUEST_HANDLE(xen_msr_entry_t);
>>>   
>>> +struct arch_physinfo {
>>> +};
>>>   #endif /* !__ASSEMBLY__ */
>> While the term "p2m_ipa_bits" surely isn't arch-agnostic, I wonder
>> whether the expressed information is (the x86 equivalent being
>> hap_paddr_bits, at a guess), and hence whether this really ought
>> to live in an arch-specific sub-struct.
> 
> Well, on Arm we calculate the number of the IPA bits based on the number 
> of PA bits when setting Stage 2 address translation.
> I might mistake, but what we currently have on Arm is "ipa_bits == 
> pa_bits". So, this means that information we need at the toolstack side 
> isn't really arch-specific and
> we could probably avoid introducing arch-specific sub-struct by suitable 
> renaming the field (pa_bits, paddr_bits, whatever).
> 
> We could even name the field as hap_paddr_bits. Although, I don't know 
> whether the hap_* is purely x86-ism, but I see there are several 
> mentions in the common code (hap_pt_share, use_hap_pt, etc). Any 
> suggestions?

Well, HAP or not - there is going to be a limit to a guest's
address bits. So I don't see why it would matter whether HAP is
an x86-specific term. If you wanted to express the guest nature
and distinguish it from "paddr_bits", how about "gaddr_bits" or
"gpaddr_bits"?

Jan