Re: [PATCH 1/2] x86/virt/tdx: Drop tdx_clflush_*()

[Nikolay Borisov]

On 22.09.26 г. 23:52 ч., Rick Edgecombe wrote:
> The TDX module exposes a bit (CLFLUSH_BEFORE_ALLOC) to say whether it
> requires some memory to be flushed from the cache before being handed
> to the TDX module.
>
> During the initial TDX upstreaming, it was decided it would be simplest
> to just always flush in these cases, rather than checking for the bit and
> having conditional logic. So currently the kernel flushes in several
> places when handing memory to the TDX module.
>
> In practice this bit has never been set by any TDX module, so flushing
> is unneeded. Going forward the TDX docs will be updated to clarify that
> CLFLUSH_BEFORE_ALLOC will never be set in any future TDX module either.
>
> So make code even simpler by just deleting all the CLFLUSH_BEFORE_ALLOC
> handling.
>
> AI was used to review the change.
>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>


The code change itself is trivial, however nothing in the code being 
removed is tied to CLFLUSH_BEFORE_ALLOC directly. And from the changelog 
it's not entirely clear which those operations are (as per other 
reviewers feedback). Looking at the TDX module spec that flag is 
mentioned in relation to the following 3 operations:

TDH.MEM.SEPT.ADD
TDH.MEM.PAGE.ADD
TDH.MEM.PAGE.AUG

Whereas the patch also removes flushing from MNG_CREATE/VP_ADDCX/MNG_ADDCX


So concrete references in the changelog would be much appreciated i.e 
whether flushing for those 3 additional functions was because people 
were overzealous, or they simply have been omitted from the public 
documentation.