linux-kernel - Re: [PATCHv11 05/19] x86/relocate_kernel: Use named labels for less confusion

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Message-ID: <20240529112852.GBZlcRdI3oqBtjKxAV@fat_crate.local>
Date: Wed, 29 May 2024 13:28:52 +0200
From: Borislav Petkov <bp@...en8.de>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>
Cc: Nikolay Borisov <nik.borisov@...e.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	Elena Reshetova <elena.reshetova@...el.com>,
	Jun Nakajima <jun.nakajima@...el.com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	"Kalra, Ashish" <ashish.kalra@....com>,
	Sean Christopherson <seanjc@...gle.com>,
	"Huang, Kai" <kai.huang@...el.com>,
	Ard Biesheuvel <ardb@...nel.org>, Baoquan He <bhe@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>, kexec@...ts.infradead.org,
	linux-hyperv@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv11 05/19] x86/relocate_kernel: Use named labels for less
 confusion

On Wed, May 29, 2024 at 02:17:29PM +0300, Kirill A. Shutemov wrote:
> > That jmp 1f becomes redundant now as it simply jumps 1 line below.
> > 
> 
> Nothing changed wrt this jump. It dates back to initial kexec
> implementation.
> 
> See 5234f5eb04ab ("[PATCH] kexec: x86_64 kexec implementation").
> 
> But I don't see functional need in it.
> 
> Anyway, it is outside of the scope of the patch.

Yap, Kirill did what Nikolay should've done - git archeology. Please
don't forget to do that next time.

And back in the day they didn't comment non-obvious things because
commenting is for losers. :-\

So that unconditional forward jump either flushes branch prediction on
some old uarch or something else weird, uarch-special.

I doubt we can remove it just like that.

Lemme add Andy - he should know.

-- 
Regards/Gruss,
    Boris.

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