> From: Dave Hansen <dave.hansen@xxxxxxxxx> > Sent: Friday, August 11, 2023 7:27 AM > [...] > On 8/10/23 19:12, Dexuan Cui wrote: > > GHCI spec for TDX 1.0 says that the MapGPA call may fail with the R10 > > error code = TDG.VP.VMCALL_RETRY (1), and the guest must retry this > > operation for the pages in the region starting at the GPA specified > > in R11. > > > > When a fully enlightened TDX guest runs on Hyper-V, Hyper-V can return > > the retry error when set_memory_decrypted() is called to decrypt up to > > 1GB of swiotlb bounce buffers. > > This changelog is not great. It gives zero background and wastes bytes > on telling me which register the error code is in (I don't care in a > changelog) and then using marketing fluff words like "fully enlightened". > > Let's stick to the facts, give some background, and also avoid > regurgitating the GHCI, eh? > > How's this? I appreciate the great changelog! Will use this in v10. > x86/tdx: Retry partially-completed page conversion hypercalls > > TDX guest memory is private by default and the VMM may not access it. > However, in cases where the guest needs to share data with the VMM, > the guest and the VMM can coordinate to make memory shared between > them. > > The guest side of this protocol includes the "MapGPA" hypercall. This > call takes a guest physical address range. The hypercall spec (aka. > the GHCI) says that the MapGPA call is allowed to return partial > progress in mapping this range and indicate that fact with a special > error code. A guest that sees such partial progress is expected to > retry the operation for the portion of the address range that was not > completed. > > Hyper-V does this partial completion dance when set_memory_decrypted() > is called to "decrypt" swiotlb bounce buffers that can be up to 1GB > in size. It is evidently the only VMM that does this, which is why > nobody noticed this until now. This clarifies the obscure "when needed" in my version by emphasizing the "partial progress". This also gives necessary background info. Thanks!
