On Fri, Nov 12, 2021 at 01:23:25PM -0800, Andy Lutomirski wrote:

SEV-SNP, TDX, and any reasonable software solution all require that the host
know which pages are private and which pages are shared.  Sure, the old
SEV-ES Linux host implementation was very simple, but it's nasty and
fundamentally can't support migration.

Right, so at least SNP guests need to track which pages have been
already PVALIDATEd by them so that they don't validate them again. So if
we track that somewhere in struct page or wherever, that same bit can be
used to state, page is private or shared.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette