Re: [PATCH] x86/stubs: Consolidate the stubs infrastructure in asm/stubs.h

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.05.2025 15:49, Andrew Cooper wrote:
> On 16/05/2025 2:41 pm, Jan Beulich wrote:
>> On 16.05.2025 15:33, Andrew Cooper wrote:
>>> --- /dev/null
>>> +++ b/xen/arch/x86/include/asm/stubs.h
>>> @@ -0,0 +1,37 @@
>>> +/* SPDX-License-Identifier: GPL-2.0-only */
>>> +#ifndef X86_ASM_STUBS_H
>>> +#define X86_ASM_STUBS_H
>>> +
>>> +/*
>>> + * Xen has several per-cpu executable stubs which are written dynamically.
>> This puts it pretty well. Yet in principle there may be further, perhaps
>> entirely different stubs in the future. Hence stubs.h feels a little
>> generic. What about exec-stubs.h?
> 
> stubs is quite generic; in fact, that was my feedback for struct stubs.
> 
> There is something to be said for the header file to be the same as the
> struct you want from it.
> 
> What did you have in mind for "different stubs"?  The only thing that
> makes these special (i.e. not regular per-cpu data) is that we need an
> executable mapping of them.  So, while I think it's reasonably likely
> that we'll gain other uses (although, we're losing LSTAR/CSTAR when FRED
> is enabled), I'm less certain what non-executable stubs would look like.

A while after having written my reply, I started wondering myself. Likely
we wouldn't normally call anything non-executable a "stub", so please
disregard my suggestion.

Jan