Re: [PATCH v10 1/2] x86/tdx: Retry partially-completed page conversion hypercalls

[Isaku Yamahata]

On Fri, Aug 11, 2023 at 02:48:25PM -0700,
Dexuan Cui <decui@xxxxxxxxxxxxx> wrote:

> 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.

Now TDX KVM + TDX qemu supports partial completion because TD guest can pass
very large range. e.g. 1GB order.  I tested this patch with (patched) TDX
KVM/qemu.

Reviewed-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
Tested-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
-- 
Isaku Yamahata <isaku.yamahata@xxxxxxxxx>