Re: [PATCH 1/2] x86/virt/tdx: Use PFN directly for mapping guest private memory

[Dave Hansen]

On 4/2/26 13:47, Sean Christopherson wrote:
> On Thu, Mar 19, 2026, Dave Hansen wrote:
>> On 3/18/26 17:57, Yan Zhao wrote:
>>> Remove the completely unnecessary assumption that memory mapped into a TDX
>>> guest is backed by refcounted struct page memory. From KVM's point of view,
>>> TDH_MEM_PAGE_ADD and TDH_MEM_PAGE_AUG are glorified writes to PTEs, so they
>>> have no business placing requirements on how KVM and guest_memfd manage
>>> memory.
>>
>> I think this goes a bit too far.
>>
>> It's one thing to say that it's more convenient for KVM to stick with
>> pfns because it's what KVM uses now. Or, that the goals of using 'struct
>> page' can be accomplished other ways. It's quite another to say what
>> other bits of the codebase have "business" doing.
>>
>> Sean, can we tone this down a _bit_ to help guide folks in the future?
> 
> I strongly disagree on this one.

I think I understand the motivation now. All I'm saying is that instead
of something like:

	Remove the completely unnecessary assumption that memory mapped
	into a TDX guest is backed by refcounted struct page memory.

I'd rather see something along the lines of

	KVM's MMUs work with PFNs. This is very much an intentional
	design choice. It ensures that the KVM MMUs remains flexible
	and are not too tied to the regular CPU MMUs and the kernel code
	around	them.

	Using 'struct page' for TDX memory is not a good fit anywhere
	near the KVM MMU code.

Would you disagree strongly with that kind of rewording?