Matias Zabaljauregui wrote:
> Jeremy, I fixed the code following your comments (hope you still
> remember).
>
> I'd like to ask you again about this one:
>
>
>>> /* Found in switcher.S */
>>> extern unsigned long default_idt_entries[];
>>> diff --git a/arch/x86/include/asm/lguest_hcall.h b/arch/x86/include/asm/lguest_hcall.h
>>> index 0f4ee71..3860153 100644
>>> --- a/arch/x86/include/asm/lguest_hcall.h
>>> +++ b/arch/x86/include/asm/lguest_hcall.h
>>> @@ -17,6 +17,7 @@
>>> #define LHCALL_SET_PMD 15
>>> #define LHCALL_LOAD_TLS 16
>>> #define LHCALL_NOTIFY 17
>>> +#define LHCALL_SET_PUD 18
>>>
>>>
>> PGD is more accurate than PUD (here, and the rest of the patch). The
>> pud level of the pagetable is the 4th level used by 64-bit; PAE just has
>> PGD, PMD and PTE levels. Due to pagetable level folding, the PGD is
>> sometimes referred to as the PUD when looking "up" the pagetable tree
>> (ie, the PUD is logically the next level up from the PMD), but its still
>> just an alias for the PGD. Since the hypervisor interface shouldn't
>> care about how the guest OS manages its pagetables, it should use a
>> consistent naming for the levels as they "really" are. Lguest
>> traditionally uses the same names that Linux does, so PGD is appropriate.
>>
>
> I understand, but then should we change also the LHCALL_SET_PMD name ?
> this is the one used for setting a new pgd when PAE is NOT activated.
>
Yeah, that would be consistent. In non-PAE, the pmd is just the next
logical level up from the pte, but just an alias name for the pgd.
> So, just to confirm: even if we are implementing pv_mmu_ops.set_pud
> replacement (lguest_set_pud in our case), we should use LHCALL_SET_PGD
> hypercall name in this code because that is what host is going to
> actually do?
>
Yeah, I guess. The set_pud notation makes some sense within Linux
because of its pagetable-folding, but the actual lguest implementation
is mapping between the guest's abstractions to the hypervisor abi's.
(In Xen this wasn't much of an issue because its the same hypercall for
updating a pagetable at any level, and the hypervisor can work out
what's going on for itself.)
J
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