Re: [PATCH 1/4] x86/entry: Make paranoid_exit() callable

[Lai Jiangshan]

On 2021/12/21 02:56, Borislav Petkov wrote:
> On Mon, Dec 13, 2021 at 11:03:37PM +0800, Lai Jiangshan wrote:
> > From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
> >
> > Move the last JMP out of paranoid_exit() and make it callable.
> >
> > It will allow asm_exc_nmi() to call it and avoid duplicated code.
> >
> > No functional change intended.
> >
> > Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/entry/entry_64.S | 18 +++++++++++-------
> >   1 file changed, 11 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> > index 44dadea935f7..3dc3cec03425 100644
> > --- a/arch/x86/entry/entry_64.S
> > +++ b/arch/x86/entry/entry_64.S
> > @@ -439,7 +439,8 @@ SYM_CODE_START(\asmsym)
> >   
> >   	call	\cfunc
> >   
> > -	jmp	paranoid_exit
> > +	call	paranoid_exit
> > +	jmp	restore_regs_and_return_to_kernel
>
> I guess but I don't like the glueing of the CALL to paranoid_exit with
> the JMP to the restore_regs_and_return_to_kernel label. That reads
> to me as, "if you're calling paranoid_exit() you must jump to the
> restore_regs_and_return_to_kernel label but not always."
>
> So I'm thinking you should leave the jump to that label inside
> paranoid_exit() and use its %rbx argument to control when to jump to it
> and when not.

Hello

Thank you for reviewing it.

This patch is a part of the job converting some ASM code to C code.  The
changelog of it in the original big patchset reads:

  Allow paranoid_exit() to be re-written in C later and also allow
  asm_exc_nmi() to call it to avoid duplicated code.

And this smaller patchset doesn't include the work of converting ASM code,
so I removed "Allow paranoid_exit() to be re-written in C later" because I
thought "allowing asm_exc_nmi() to call it and avoiding duplicated code" is
enough to justify the value of this change.

When paranoid_exit() is ready to be converted to C, it can't have jump to
any label that is not in paranoid_exit() itself.

I'm sorry to not have put all of the intents in the changelog:

-It will allow asm_exc_nmi() to call it and avoid duplicated code.
+It will allow asm_exc_nmi() to call it and avoid duplicated code and allow
+future work to convert paranoid_exit() to C code.

Thanks
Lai