Re: [PATCH v6 01/21] x86/tdx: Use enum to define page level of TDX supported page sizes

[Huang, Kai]

On Thu, 2022-10-27 at 16:51 +0300, Kirill A. Shutemov wrote:
> On Thu, Oct 27, 2022 at 08:42:16AM +0000, Huang, Kai wrote:
> > On Thu, 2022-10-27 at 15:08 +0800, Li, Xiaoyao wrote:
> > > > @@ -663,27 +662,16 @@ static bool try_accept_one(phys_addr_t *start,
> > > > unsigned long len,
> > > >    	if (len < accept_size)
> > > >    		return false;
> > > >    
> > > > +	/* TDX only supports 4K/2M/1G page sizes */
> > > 
> > > yes, a page can be mapped as 1G size to TD via secure/shared EPT. But 
> > > for this particular TDX_ACCEPT_PAGE case, it only supports 4K and 2M 
> > > currently, which is defined in TDX module spec.
> > 
> > I checked the TDX module public spec, and it appears you are right.  But I am
> > not sure whether it will be changed in the future?
> 
> The spec says:
> 
> 	Level of the Secure EPT entry that maps the private page to be
> 	accepted: either 0 (4KB) or 1 (2MB) – see 20.5.1
> 
> Yes, it is about 4k and 2M, but it also refers 20.5.1, which lists sizes
> up to 16PB.

Also, I think we are mixing two things: 1) leaf page sizes  (4K/2M/1G);  2) page
table levels.  The latter has more levels than the former.  For try_accept_one()
(and TDX host code), we actually care only about the former.

KVM needs the latter (or both), so it's better for KVM to handle on its own.

> 
> Ultimately, it does not matter: if TDX module doesn't support the size or
> cannot accept the memory for other reason guest kernel will fallback to
> smaller size.
> 

Yes.