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Message-ID: <CAMj1kXESAk4ZT_HAFaWQJLmyo9CyFYbRsToEXagPygBpFhDZiw@mail.gmail.com> Date: Sat, 10 May 2025 16:51:07 +0200 From: Ard Biesheuvel <ardb@...nel.org> To: David Laight <david.laight.linux@...il.com> 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> Subject: Re: [RFC PATCH 2/3] x86/boot: Set __pgtable_l5_enabled correctly before calling into C code On Sat, 10 May 2025 at 15:54, David Laight <david.laight.linux@...il.com> wrote: > > On Tue, 6 May 2025 17:45:35 +0200 > Ard Biesheuvel <ardb+git@...gle.com> wrote: > > > From: Ard Biesheuvel <ardb@...nel.org> > > > > Ensure that __pgtable_l5_enabled() is set to its permanent value before > > calling into any C code that may manipulate page tables or reference any > > global variable or object that may be dimensioned differently based on > > whether 5-level paging is in use. > ... > > #ifdef CONFIG_X86_5LEVEL > > -/* __pgtable_l5_enabled needs to be in .data to avoid being cleared along with .bss */ > > -unsigned int __section(".data") __pgtable_l5_enabled; > > +unsigned int __pgtable_l5_enabled = 1; > > + > > +/* These need to be in .data to avoid being cleared along with .bss */ > > unsigned int __section(".data") pgdir_shift = 39; > > unsigned int __section(".data") ptrs_per_p4d = 1; > > Is that comment (and the section assignment) relevant given that they > are initialised non-zero? > Excellent point - no, they are not. > I'd guess that __pgtable_l5_enabled was getting set before .bss was cleared? > Yes.
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