linux-kernel - Re: [RFC PATCH 1/7] x86/entry: Move PUSH_AND_CLEAR_REGS out of paranoid

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Message-ID: <20230406203738.GE405948@hirez.programming.kicks-ass.net>
Date:   Thu, 6 Apr 2023 22:37:38 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        "H. Peter Anvin" <hpa@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Andy Lutomirski <luto@...nel.org>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Cfir Cohen <cfir@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        David Kaplan <David.Kaplan@....com>,
        David Rientjes <rientjes@...gle.com>,
        Dirk Hohndel <dirkhh@...are.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Jiri Slaby <jslaby@...e.cz>, Joerg Roedel <joro@...tes.org>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Stunes <mstunes@...are.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Tony Luck <tony.luck@...el.com>, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, x86@...nel.org,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC PATCH 1/7] x86/entry: Move PUSH_AND_CLEAR_REGS out of
 paranoid_entry

On Mon, Apr 03, 2023 at 10:05:59PM +0800, Lai Jiangshan wrote:
> @@ -915,11 +922,8 @@ SYM_CODE_END(xen_failsafe_callback)
>   * R14 - old CR3
>   * R15 - old SPEC_CTRL
>   */
> -SYM_CODE_START(paranoid_entry)
> +SYM_FUNC_START(paranoid_entry)
>  	ANNOTATE_NOENDBR
> -	UNWIND_HINT_FUNC

That isn't quite equivalent. SYM_FUNC_START() gets you ENDBR, while the
SYM_CODE_START(); ANNOTATE_NOENDBR; UNWIND_HINT_FUNC is
explicitly no ENDBR.


> -	PUSH_AND_CLEAR_REGS save_ret=1
> -	ENCODE_FRAME_POINTER 8
>  
>  	/*
>  	 * Always stash CR3 in %r14.  This value will be restored,