linux-kernel - Re: [PATCH V4 04/50] x86/xen: Add xenpv_restore_regs_and_return_to

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Message-ID: <YYFKy/KM7wRUg5mq@zn.tnic>
Date:   Tue, 2 Nov 2021 15:27:23 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Jan Beulich <jbeulich@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Juergen Gross <jgross@...e.com>,
        xen-devel@...ts.xenproject.org, Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Subject: Re: [PATCH V4 04/50] x86/xen: Add
 xenpv_restore_regs_and_return_to_usermode()

On Tue, Nov 02, 2021 at 12:22:50PM +0100, H. Peter Anvin wrote:
> It would be interesting to have an "override function with jmp"
> alternatives macro. It doesn't require any changes to the alternatives
> mechanism proper (but possibly to objtool): it would just insert an
> alternatives entry without adding any code including nops to the main
> path. It would of course only be applicable to a jmp, so a syntax like
> OVERRIDE_JMP feature, target rather than open-coding the instruction
> would probably be a good idea.

I think you wanna say ALTERNATIVE_JMP here seeing how we have
ALTERNATIVE_CALL already :)

As to marking it properly, we can finally add that struct
alt_instr.flags thing we have been trying to add for years now.

/me adds it to his evergrowing todo.

If anyone beats /me to it, /me will gladly have a look at it.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette