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

[Kirill A. Shutemov]

On Tue, Jan 31, 2023 at 09:32:37AM +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

Oops, just noticed a typo. s/in/is/

> > __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.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Fixes: c30c4b2555ba ("x86/tdx: Refactor __tdx_hypercall() to allow pass down more arguments")
> > Link: https://lore.kernel.org/all/202301290255.buUBs99R-lkp@xxxxxxxxx
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > ---
> > 
> > The patch is against tip/x86/tdx. tip/sched/core removes
> > TDX_HCALL_ISSUE_STI. The trird hunk of the patch is not relevant
> > after that.
> 
> Right, this should work. But it does leave me wondering, should we
> perhaps strive to completely remove the flags thing and move to
> __tdx_hypercall() and __tdx_hypercall_ret() or something? That is,
> simply have two different functions, one with and one without return
> data.
> 
> It should be trivial to generate that without actual code duplication.

Yeah, that's doable. I will give it a try. I guess on top this one (plus
sched/core changes) should be.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov