Re: [PATCH v10 05/16] x86/virt/tdx: Add skeleton to enable TDX on demand

[Isaku Yamahata]

On Mon, Mar 13, 2023 at 10:45:45PM -0700,
Dave Hansen <dave.hansen@xxxxxxxxx> wrote:

> On 3/13/23 21:02, Isaku Yamahata wrote:
> >> Then it is a hidden behaviour of the TDX module that is not reflected in the
> >> spec.  I am not sure whether we should handle because: 
> >>
> >> 1) This is an extremely rare case.  Kernel would be basically under attack if
> >> such error happened.  In the current series we don't handle such case in
> >> KEY.CONFIG either but just leave a comment (see patch 13).
> >>
> >> 2) Not sure whether this will be changed in the future.
> >>
> >> So I think we should keep as is.
> > TDX 1.5 spec introduced TDX_RND_NO_ENTROPY status code.  For TDX 1.0, let's
> > postpone it to TDX 1.5 activity.
> 
> What the heck does this mean?
> 
> I don't remember seeing any code here that checks for "TDX 1.0" or "TDX
> 1.5".  That means that this code needs to work with _any_ TDX version.
> 
> Are features being added to new versions that break code written for old
> versions?

No new feature, but new error code. TDX_RND_NO_ENTROPY, lack of entropy.
For TDX 1.0, some APIs return TDX_SYS_BUSY. It can be contention(lock failure)
or the lack of entropy.  The caller can't distinguish them.
For TDX 1.5, they return TDX_RND_NO_ENTROPY instead of TDX_SYS_BUSY in the case
of rdrand/rdseed failure.

Because both TDX_SYS_BUSY and TDX_RND_NO_ENTROPY are recoverable error
(bit 63 error=1, bit 62 non_recoverable=0), the caller can check error bit and
non_recoverable bit for retry.
-- 
Isaku Yamahata <isaku.yamahata@xxxxxxxxx>