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SubjectRe: [PATCH v3 07/12] x86/tdx: Make TDX_HYPERCALL asm similar to TDX_MODULE_CALL
On Thu, Jul 27, 2023 at 11:05:35PM +0000, Huang, Kai wrote:
> On Thu, 2023-07-27 at 20:10 +0300, kirill.shutemov@linux.intel.com wrote:
> > On Wed, Jul 26, 2023 at 11:25:09PM +1200, Kai Huang wrote:
> > >
> > > Remove the __tdx_hypercall_ret() as __tdx_hypercall() already does so.
> >
> > Hm. So we now update struct on all VMCALLs. Is it a good idea? 
> >
>
> Do you mean we "unconditionally save output registers to the structure", right?
>
> > We give
> > more control to VMM where it is not needed. 
> >
>
> I don't quite follow this. Can you elaborate?
>
> Do you worry about VMM being malicious and putting malicious values to the
> registers?

Yes. Caller of the hypercall may expect that the register is in-only and
re-use the field for other stuff. And it would work until VMM decide
otherwise.

> > I would rather keep the struct
> > read-only where possible.
> >
>
> We can achieve this if there's a clean way to do, but I don't see that.

Keep _ret() and non-_ret() versions?

--
Kiryl Shutsemau / Kirill A. Shutemov

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