Re: [PATCH v2 1/4] x86/tdx: Use PFN directly for mapping guest private memory

[Ackerley Tng]

Yan Zhao <yan.y.zhao@xxxxxxxxx> writes:

> From: Sean Christopherson <seanjc@xxxxxxxxxx>
>
> Remove struct page assumptions/constraints in the SEAMCALL wrapper APIs for
> mapping guest private memory and have them take PFN directly.
>

Thanks for this :)

> Having core TDX make assumptions that guest private memory must be backed
> by struct page (and/or folio) will create subtle dependencies on how
> KVM/guest_memfd allocates/manages memory (e.g., whether it uses memory
> allocated from core MM, if the memory is refcounted, or if the folio is
> split) that are easily avoided. [1].
>
> KVM's MMUs work with PFNs. This is very much an intentional design choice.
> It ensures that the KVM MMUs remain flexible and are not too tied to the
> regular CPU MMUs and the kernel code around them. Using 'struct page' for
> TDX guest memory is not a good fit anywhere near the KVM MMU code [2].
>
> Use "kvm_pfn_t pfn" for type safety. Using this KVM type is appropriate
> since APIs tdh_mem_page_add() and tdh_mem_page_aug() are exported to KVM
> only.
>
> [ Yan: Replace "u64 pfn" with "kvm_pfn_t pfn" ]
>

Thanks for your help, Yan!

Reviewed-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>

> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
> Link: https://lore.kernel.org/all/aWgyhmTJphGQqO0Y@xxxxxxxxxx [1]
> Link: https://lore.kernel.org/all/ac7V0g2q2hN3dU5u@xxxxxxxxxx [2]
>
> [...snip...]
>