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

[Oleksandr <olekstysh@gmail.com>]

On 30.08.21 16:16, Jan Beulich wrote:

Hi Jan

> 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.

agree


>   If you wanted to express the guest nature
> and distinguish it from "paddr_bits", how about "gaddr_bits" or
> "gpaddr_bits"?

ok, both sound fine to me, with a little preference for gpaddr_bits. So, 
will drop arch-specific sub-struct for the next version.

Thank you.


>
> Jan
>
-- 
Regards,

Oleksandr Tyshchenko