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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a1f58f2961sm6429607f8f.45.2025.05.10.06.54.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 10 May 2025 06:54:50 -0700 (PDT) Date: Sat, 10 May 2025 14:54:49 +0100 From: David Laight To: Ard Biesheuvel Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Ard Biesheuvel , Ingo Molnar , Linus Torvalds Subject: Re: [RFC PATCH 2/3] x86/boot: Set __pgtable_l5_enabled correctly before calling into C code Message-ID: <20250510145449.4117af82@pumpkin> In-Reply-To: <20250506154532.1281909-7-ardb+git@google.com> References: <20250506154532.1281909-5-ardb+git@google.com> <20250506154532.1281909-7-ardb+git@google.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 6 May 2025 17:45:35 +0200 Ard Biesheuvel wrote: > From: Ard Biesheuvel > > 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? I'd guess that __pgtable_l5_enabled was getting set before .bss was cleared? David