From: Nathan Chancellor <nathan@kernel.org>
To: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
dave.hansen@linux.intel.com
Cc: x86@kernel.org, hpa@zytor.com, ndesaulniers@google.com,
morbo@google.com, justinstitt@google.com, song@kernel.org,
ribalda@chromium.org, linux-kernel@vger.kernel.org,
llvm@lists.linux.dev, patches@lists.linux.dev,
ns <0n-s@users.noreply.github.com>,
Nathan Chancellor <nathan@kernel.org>
Subject: [PATCH 0/2] x86/purgatory: Avoid kexec runtime warning with LLVM 18
Date: Wed, 17 Apr 2024 14:53:44 -0700 [thread overview]
Message-ID: <20240417-x86-fix-kexec-with-llvm-18-v1-0-5383121e8fb7@kernel.org> (raw)
Hi all,
After LLVM commit d8a04398f949 ("Reland [X86] With large code model, put
functions into .ltext with large section flag (#73037)") [1], which
landed in the 18.x cycle, there is a runtime warning when loading a
kernel via kexec due to the presence of two text sections (.text and
.ltext).
$ kexec -l /boot/vmlinuz-linux --initrd=/boot/initramfs-linux.img --reuse-cmdline
$ dmesg -l warn+
...
[ 1.264240] ------------[ cut here ]------------
[ 1.264647] WARNING: CPU: 0 PID: 96 at kernel/kexec_file.c:945 kexec_load_purgatory+0x2c8/0x3c0
[ 1.265322] Modules linked in:
[ 1.265565] CPU: 0 PID: 96 Comm: kexec Not tainted 6.9.0-rc4-00031-g96fca68c4fbf #1 eae91b3fe699ecba2dd0a886471788e49eb36ac0
[ 1.266403] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 1.267268] RIP: 0010:kexec_load_purgatory+0x2c8/0x3c0
[ 1.267661] Code: 54 24 0c 48 89 c8 48 29 d0 0f 82 5d ff ff ff 49 03 54 24 1c 48 39 d1 0f 83 4f ff ff ff 49 8b 17 48 39 4a 18 0f 84 30 ff ff ff <0f> 0b e9 3b ff ff ff 66 85 c9 74 18 48 8b 5a 28 48 01 d3 45 31 e4
[ 1.269052] RSP: 0018:ffffbe28007cfb50 EFLAGS: 00010206
[ 1.269447] RAX: 0000000000000000 RBX: 00000000000000d0 RCX: 0000000000000000
[ 1.269982] RDX: ffff988c8174d000 RSI: 0000000000000010 RDI: ffffbe2801d940c0
[ 1.270527] RBP: 0000000000000002 R08: 0000003d8b4c0000 R09: cc0000000025ff00
[ 1.271063] R10: 0000003d8b4c0000 R11: cc0000000025ff00 R12: ffffbe28000d5084
[ 1.271603] R13: 000000013ffff000 R14: ffff988c8174d000 R15: ffffbe28007cfbe0
[ 1.272140] FS: 00007fec73535740(0000) GS:ffff988cbbc00000(0000) knlGS:0000000000000000
[ 1.272744] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1.273178] CR2: 00007fec736b1390 CR3: 0000000101a24000 CR4: 0000000000350ef0
[ 1.273732] Call Trace:
[ 1.273929] <TASK>
[ 1.274100] ? __warn+0xc9/0x1c0
[ 1.274356] ? kexec_load_purgatory+0x2c8/0x3c0
[ 1.274704] ? report_bug+0x139/0x1e0
[ 1.274998] ? handle_bug+0x42/0x70
[ 1.275269] ? exc_invalid_op+0x1a/0x50
[ 1.275574] ? asm_exc_invalid_op+0x1a/0x20
[ 1.275900] ? kexec_load_purgatory+0x2c8/0x3c0
[ 1.276251] bzImage64_load+0x1c1/0x6a0
[ 1.276556] kexec_image_load_default+0x49/0x60
[ 1.276907] __se_sys_kexec_file_load+0x606/0x790
[ 1.277280] ? arch_exit_to_user_mode_prepare+0x6e/0x70
[ 1.277675] do_syscall_64+0x90/0x170
[ 1.277955] ? srso_return_thunk+0x5/0x5f
[ 1.278265] ? __count_memcg_events+0x50/0xc0
[ 1.278597] ? srso_return_thunk+0x5/0x5f
[ 1.278901] ? handle_mm_fault+0xb18/0x11c0
[ 1.279218] ? vfs_read+0x2c8/0x2f0
[ 1.279498] ? srso_return_thunk+0x5/0x5f
[ 1.279802] ? do_user_addr_fault+0x4d2/0x690
[ 1.280138] ? srso_return_thunk+0x5/0x5f
[ 1.280449] ? srso_return_thunk+0x5/0x5f
[ 1.280755] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 1.281136] RIP: 0033:0x7fec7363e88d
[ 1.281411] Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 73 14 0d 00 f7 d8 64 89 01 48
[ 1.282789] RSP: 002b:00007ffd136f4808 EFLAGS: 00000246 ORIG_RAX: 0000000000000140
[ 1.283354] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fec7363e88d
[ 1.283893] RDX: 00000000000000c5 RSI: 0000000000000005 RDI: 0000000000000003
[ 1.284427] RBP: 0000000000000003 R08: 0000000000000000 R09: 00005628517eef10
[ 1.284966] R10: 00005628580a75f0 R11: 0000000000000246 R12: 0000000000000003
[ 1.285500] R13: 00005628517f89a8 R14: 00007ffd136f4b98 R15: 0000000000000004
[ 1.286036] </TASK>
[ 1.286210] ---[ end trace 0000000000000000 ]---
Unlike LTO and PGO, which were disabled for the purgatory in commit
97b6b9cbba40 ("x86/purgatory: remove PGO flags") and commit 75b2f7e4c9e0
("x86/purgatory: Remove LTO flags"), this optimization has no flag to
opt out of it. One way to resolve this would be to use '.ltext' and
'.lrodata' as the text and read-only data sections in the out of line
assembly in arch/x86/purgatory but there is nothing that stops future
changes from splitting the text section further.
Properly avoid the warning by using a linker script to coalesce all
separate text sections into one, which was alluded to by both the change
that introduced the warning and 75b2f7e4c9e0... I think this really
should have been done then but I wasn't looking too far ahead :) To
avoid backsliding now that all sections are properly described by the
linker script, turn on orphan section warnings as well.
[1]: https://github.com/llvm/llvm-project/commit/d8a04398f9492f043ffd8fbaf2458778f7d0fcd5
---
Nathan Chancellor (2):
x86/purgatory: Add a linker script
x86/purgatory: Enable orphan section warnings
arch/x86/purgatory/.gitignore | 1 +
arch/x86/purgatory/Makefile | 19 +++---------
arch/x86/purgatory/purgatory.lds.S | 63 ++++++++++++++++++++++++++++++++++++++
3 files changed, 69 insertions(+), 14 deletions(-)
---
base-commit: 0bbac3facb5d6cc0171c45c9873a2dc96bea9680
change-id: 20240416-x86-fix-kexec-with-llvm-18-c986b21845c5
Best regards,
--
Nathan Chancellor <nathan@kernel.org>
next reply other threads:[~2024-04-17 21:54 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-17 21:53 Nathan Chancellor [this message]
2024-04-17 21:53 ` [PATCH 1/2] x86/purgatory: Add a linker script Nathan Chancellor
2024-04-17 21:53 ` [PATCH 2/2] x86/purgatory: Enable orphan section warnings Nathan Chancellor
2024-04-18 11:14 ` [PATCH 0/2] x86/purgatory: Avoid kexec runtime warning with LLVM 18 Borislav Petkov
2024-04-18 15:15 ` Nathan Chancellor
2024-04-18 15:44 ` Nick Desaulniers
2024-04-18 15:59 ` Ard Biesheuvel
2024-04-18 17:52 ` Ard Biesheuvel
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