linux-kernel - Re: [PATCHv4, REBASED 1/4] x86/mm/ident_map: Fix virtual address wrap to zero

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Message-ID: <qz42rystorh4q2fpk5kpgjnycorfjmjypjgj3dmi4hhfznlzdx@eaertxsby5st>
Date: Mon, 4 Nov 2024 11:26:55 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Andy Lutomirski <luto@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Baoquan He <bhe@...hat.com>, Ard Biesheuvel <ardb@...nel.org>, 
	Tom Lendacky <thomas.lendacky@....com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, Sean Christopherson <seanjc@...gle.com>, 
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org, Kai Huang <kai.huang@...el.com>
Subject: Re: [PATCHv4, REBASED 1/4] x86/mm/ident_map: Fix virtual address
 wrap to zero

On Thu, Oct 31, 2024 at 02:59:16PM +0100, Borislav Petkov wrote:
> On Thu, Oct 31, 2024 at 12:11:52PM +0200, Kirill A. Shutemov wrote:
> > Do we have magic words for that?
> 
> No clue.
> 
> > I tried to express that in the second paragraph: "no such users in the
> > upstream".
> 
> Right, so perhaps better to spell it out explicitly:
> 
> "Backporter's note:
> 
> This fixes a theoretical issue only and there's no need to backport it to
> stable."
> 
> at the end of the commit message.

Okay.

> 
> > > And which commit is it fixing?
> > > 
> > > aece27851d44 ("x86, 64bit, mm: Add generic kernel/ident mapping helper")
> > > perhaps?
> > 
> > This one is closer:
> > 
> > e4630fdd4763 ("x86/power/64: Always create temporary identity mapping correctly")
> > 
> > It adds x86_mapping_info::offset.
> 
> But aece27851d44 has the faulty check...

It cannot be triggered without 'offset'.

I'll put both.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov