Re: [PATCH v19 058/130] KVM: x86/mmu: Add a private pointer to struct kvm_mmu_page

Edgecombe, Rick P
2024-03-14T21:40:01Z

On Fri, 2024-03-15 at 10:23 +1300, Huang, Kai wrote:
> We have 3 page tables as you mentioned:
>
> PT: page table
> - Shared PT is visible to KVM and it is used by CPU.
> - Private PT is used by CPU but it is invisible to KVM.
> - Dummy PT is visible to KVM but not used by CPU.  It is used to
>    propagate PT change to the actual private PT which is used by CPU.
>
> If I recall correctly, we used to call the last one "mirrored
> (private)
> page table".
>
> I lost the tracking when we changed to use "dummy page table", but it
> seems to me "mirrored" is better than "dummy" because the latter
> means
> it is useless but in fact it is used to propagate changes to the real
> private page table used by hardware.

Mirrored makes sense to me. So like:

Private - Table actually mapping private alias, in TDX module
Shared - Shared alias table, visible in KVM
Mirror - Mirroring private, visible in KVM

>
> Btw, one nit, perhaps:
>
> "Shared PT is visible to KVM and it is used by CPU." -> "Shared PT is
> visible to KVM and it is used by CPU for shared mappings".
>
> To make it more clearer it is used for "shared mappings".
>
> But this may be unnecessary to others, so up to you.

Yep, this seems clearer.