Re: [PATCH v10 21/45] x86/mm: Add support to validate memory when changing C-bit

Borislav Petkov
2022-02-13T12:15:42Z

On Fri, Feb 11, 2022 at 11:27:54AM -0600, Brijesh Singh wrote:
> > Simply have them always present. They will have !0 values on the
> > respective guest types and 0 otherwise. This should simplify a lot of
> > code and another unconditionally present u64 won't be the end of the
> > world.
> >
> > Any other aspect I'm missing?
>
> I think that's mostly about it. IIUC, the recommendation is to define a
> new callback in x86_platform_op. The callback will be invoked
> unconditionally; The default implementation for this callback is NOP;
> The TDX and SEV will override with the platform specific implementation.
> I think we may able to handle everything in one callback hook but having
> pre and post will be a more desirable. Here is why I am thinking so:
>
> * On SNP, the page must be invalidated before clearing the _PAGE_ENC
> from the page table attribute
>
> * On SNP, the page must be validated after setting the _PAGE_ENC in the
> page table attribute.

Right, we could have a pre- and post- callback, if that would make
things simpler/clearer.

Also, in thinking further about the encryption mask, we could make it a
*single*, *global* variable called cc_mask which each guest type sets it
as it wants to.

Then, it would use it in the vendor-specific encrypt/decrypt helpers
accordingly and that would simplify a lot of code. And we can get rid of
all the ifdeffery around it too.

So I think the way to go should be we do the common functionality, I
queue it on the common tip:x86/cc branch and then SNP and TDX will be
both based ontop of it.

Thoughts?

--
Regards/Gruss,
Boris.