Re: [PATCH] x86/tdx: Do not corrupt frame-pointer in __tdx_hypercall()

[Peter Zijlstra]

On Tue, Jan 31, 2023 at 11:39:01AM +0300, Kirill A. Shutemov wrote:
> On Tue, Jan 31, 2023 at 09:34:12AM +0100, Peter Zijlstra wrote:
> > On Mon, Jan 30, 2023 at 04:53:54PM +0300, Kirill A. Shutemov wrote:
> > > If compiled with CONFIG_FRAME_POINTER=y, objtool in not happy that
> > > __tdx_hypercall() messes up RBP.
> > > 
> > >   objtool: __tdx_hypercall+0x7f: return with modified stack frame
> > > 
> > > Rework the function to store TDX_HCALL_ flags on stack instead of RBP.
> > 
> > Also, on IRC you mentioned that per TDX spec, BP is a valid argument
> > register too and you were going to raise this and get it fixed, TDX
> > hypercalls must not use BP to pass data.
> 
> I've raised the question yesterday. No progress so far. It will take time
> to get it into the public spec.

Sure, just making sure it's not forgotten about. Thanks!