Re: [RFC PATCH v4 18/36] i386/tdx: Skip BIOS shadowing setup

[Gerd Hoffmann]

On Fri, Jul 29, 2022 at 03:14:02PM +0800, Xiaoyao Li wrote:
> On 5/30/2022 7:49 PM, Gerd Hoffmann wrote:
> > On Thu, May 26, 2022 at 10:48:56AM +0800, Xiaoyao Li wrote:
> > > On 5/24/2022 3:08 PM, Gerd Hoffmann wrote:
> > > > On Thu, May 12, 2022 at 11:17:45AM +0800, Xiaoyao Li wrote:
> > > > > TDX guest cannot go to real mode, so just skip the setup of isa-bios.
> > > > 
> > > > Does isa-bios setup cause any actual problems?
> > > > (same question for patch #19).

> > There is no need for copying, end_of_1M is a alias memory region for
> > end_of_4G, so the backing storage is the same.
> 
> It is a reason that current alias approach cannot work for TDX. Because in
> TDX a private page can be only mapped to one gpa.

Ok, so memory aliasing not being supported by TDX is the underlying
reason.

> So for simplicity, I will
> just skip isa-bios shadowing for TDX instead of implementing a non-alias +
> memcpy approach.

Makes sense given that tdx wouldn't use the mapping below 1M anyway.
A comment explaining the tdx aliasing restriction would be good to make
clear why the special case for tdx exists.

take care,
  Gerd