linux-kernel - Re: [PATCH v5 3/7] x86/mm: Define PTRS_PER_P4D in terms of pgdir

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Message-ID: <CAMj1kXH2vD4VWMNroScbf1KpnODR4TW5MryTYOXchmso0yjimw@mail.gmail.com>
Date: Tue, 20 May 2025 13:29:20 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: "Kirill A. Shutemov" <kirill@...temov.name>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org, x86@...nel.org, 
	Ingo Molnar <mingo@...nel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Brian Gerst <brgerst@...il.com>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v5 3/7] x86/mm: Define PTRS_PER_P4D in terms of pgdir_shift()

On Tue, 20 May 2025 at 13:08, Kirill A. Shutemov <kirill@...temov.name> wrote:
>
> On Tue, May 20, 2025 at 12:41:42PM +0200, Ard Biesheuvel wrote:
> > @@ -61,7 +59,7 @@ extern unsigned int ptrs_per_p4d;
> >   */
> >  #define P4D_SHIFT            39
> >  #define MAX_PTRS_PER_P4D     512
> > -#define PTRS_PER_P4D         ptrs_per_p4d
> > +#define PTRS_PER_P4D         (pgdir_shift() & 1 ?: MAX_PTRS_PER_P4D)
>
> "& 1" is a hack and at least deserves a comment.
>

Fair enough.