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From: Arnd Bergmann <arnd@kernel.org>
To: Ard Biesheuvel <ardb@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, Nathan Chancellor <natechancellor@gmail.com>,
	Nick Desaulniers <ndesaulniers@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>, Darren Hart <dvhart@infradead.org>,
	Andy Shevchenko <andy@infradead.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: [PATCH] x86: efi: avoid BUILD_BUG_ON() for non-constant p4d_index
Date: Thu,  7 Jan 2021 23:34:15 +0100
Message-ID: <20210107223424.4135538-1-arnd@kernel.org> (raw)

From: Arnd Bergmann <arnd@arndb.de>

When 5-level page tables are enabled, clang triggers a BUILD_BUG_ON():

x86_64-linux-ld: arch/x86/platform/efi/efi_64.o: in function `efi_sync_low_kernel_mappings':
efi_64.c:(.text+0x22c): undefined reference to `__compiletime_assert_354'

Use the same method as in commit c65e774fb3f6 ("x86/mm: Make PGDIR_SHIFT
and PTRS_PER_P4D variable") and change it to MAYBE_BUILD_BUG_ON(),
so it only triggers for constant input.

Link: https://github.com/ClangBuiltLinux/linux/issues/256
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/x86/platform/efi/efi_64.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index e1e8d4e3a213..62bb1616b4a5 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -137,8 +137,8 @@ void efi_sync_low_kernel_mappings(void)
 	 * As with PGDs, we share all P4D entries apart from the one entry
 	 * that covers the EFI runtime mapping space.
 	 */
-	BUILD_BUG_ON(p4d_index(EFI_VA_END) != p4d_index(MODULES_END));
-	BUILD_BUG_ON((EFI_VA_START & P4D_MASK) != (EFI_VA_END & P4D_MASK));
+	MAYBE_BUILD_BUG_ON(p4d_index(EFI_VA_END) != p4d_index(MODULES_END));
+	MAYBE_BUILD_BUG_ON((EFI_VA_START & P4D_MASK) != (EFI_VA_END & P4D_MASK));
 
 	pgd_efi = efi_pgd + pgd_index(EFI_VA_END);
 	pgd_k = pgd_offset_k(EFI_VA_END);
-- 
2.29.2


             reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-07 22:34 Arnd Bergmann [this message]
2021-01-07 22:42 ` Nathan Chancellor
2021-01-13 17:51 ` Ard Biesheuvel
2021-01-15 18:23 ` Borislav Petkov
2021-01-15 18:32   ` Nathan Chancellor
2021-01-15 19:07     ` Borislav Petkov
2021-01-15 19:11       ` Arvind Sankar
2021-01-15 19:18         ` Borislav Petkov
2021-01-15 19:54           ` Arnd Bergmann
2021-01-15 20:12             ` Arvind Sankar
2021-01-15 20:32               ` Arvind Sankar
2021-01-15 19:07 ` Arvind Sankar
2021-01-15 20:27   ` Arvind Sankar
2021-01-16 16:34     ` Ard Biesheuvel
2021-01-18 20:24       ` Borislav Petkov
2021-01-18 21:42         ` Arvind Sankar
2021-01-20  9:33           ` Ard Biesheuvel
2021-01-20 11:44             ` Borislav Petkov
2021-02-03 18:51             ` Nathan Chancellor
2021-02-03 20:29               ` Ard Biesheuvel
2021-02-04 10:51                 ` Borislav Petkov
2021-02-04 10:59                   ` Ard Biesheuvel
2021-02-04 19:16                   ` Nathan Chancellor
2021-02-04 21:43                   ` Arvind Sankar
2021-02-04 22:13                     ` Borislav Petkov
2021-02-05  0:08                       ` Arvind Sankar
2021-02-05 11:39                         ` [PATCH] x86/efi: Remove EFI PGD build time checks Borislav Petkov
2021-02-05 11:57                           ` Ard Biesheuvel
2021-02-05 18:14                           ` Nick Desaulniers
2021-02-05 18:56                           ` Nathan Chancellor
2021-02-05 10:34               ` [PATCH] x86: efi: avoid BUILD_BUG_ON() for non-constant p4d_index Borislav Petkov
2021-02-05 18:27                 ` Nick Desaulniers
2021-02-05 18:31                   ` Nathan Chancellor
2021-01-20 11:26           ` Kirill A. Shutemov
2021-01-20 11:06   ` Kirill A. Shutemov

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