From: "H. Peter Anvin" <hpa@zytor.com>
To: David Laight <david.laight.linux@gmail.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
Ard Biesheuvel <ardb@kernel.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Xiongwei Song <xiongwei.song@windriver.com>,
Xin Li <xin3.li@intel.com>,
"Mike Rapoport (IBM)" <rppt@kernel.org>,
Brijesh Singh <brijesh.singh@amd.com>,
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Tony Luck <tony.luck@intel.com>,
Alexey Kardashevskiy <aik@amd.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jonathan Corbet <corbet@lwn.net>,
Sohil Mehta <sohil.mehta@intel.com>,
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Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
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Huang Shijie <shijie@os.amperecomputing.com>,
Geert Uytterhoeven <geert+renesas@glider.be>,
Namhyung Kim <namhyung@kernel.org>,
Arnaldo Carvalho de Melo <acme@redhat.com>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-efi@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv9 02/16] x86/alternatives: Disable LASS when patching kernel alternatives
Date: Mon, 28 Jul 2025 12:28:33 -0700 [thread overview]
Message-ID: <98BE7799-DA6C-4267-9E03-E6F68263D250@zytor.com> (raw)
In-Reply-To: <20250728201137.113d0f45@pumpkin>
On July 28, 2025 12:11:37 PM PDT, David Laight <david.laight.linux@gmail.com> wrote:
>On Mon, 7 Jul 2025 11:03:02 +0300
>"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> wrote:
>
>> From: Sohil Mehta <sohil.mehta@intel.com>
>>
>> For patching, the kernel initializes a temporary mm area in the lower
>> half of the address range. See commit 4fc19708b165 ("x86/alternatives:
>> Initialize temporary mm for patching").
>>
>> Disable LASS enforcement during patching to avoid triggering a #GP
>> fault.
>>
>> The objtool warns due to a call to a non-allowed function that exists
>> outside of the stac/clac guard, or references to any function with a
>> dynamic function pointer inside the guard. See the Objtool warnings
>> section #9 in the document tools/objtool/Documentation/objtool.txt.
>>
>> Considering that patching is usually small, replace the memcpy() and
>> memset() functions in the text poking functions with their open coded
>> versions.
>...
>
>Or just write a byte copy loop in C with (eg) barrier() inside it
>to stop gcc converting it to memcpy().
>
> David
Great. It's rep movsb without any of the performance.
next prev parent reply other threads:[~2025-07-28 19:29 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20250707080317.3791624-1-kirill.shutemov@linux.intel.com>
[not found] ` <20250707080317.3791624-6-kirill.shutemov@linux.intel.com>
2025-07-09 1:27 ` [PATCHv9 05/16] efi: Disable LASS around set_virtual_address_map() EFI call Sohil Mehta
[not found] ` <20250707080317.3791624-12-kirill.shutemov@linux.intel.com>
2025-07-09 2:40 ` [PATCHv9 11/16] x86/traps: Communicate a LASS violation in #GP message Sohil Mehta
2025-07-09 9:31 ` Kirill A. Shutemov
2025-07-09 9:36 ` Geert Uytterhoeven
2025-07-09 9:51 ` Kirill A. Shutemov
[not found] ` <20250707080317.3791624-13-kirill.shutemov@linux.intel.com>
2025-07-09 4:59 ` [PATCHv9 12/16] x86/traps: Generalize #GP address decode and hint code Sohil Mehta
[not found] ` <20250707080317.3791624-17-kirill.shutemov@linux.intel.com>
2025-07-09 5:31 ` [PATCHv9 16/16] x86: Re-enable Linear Address Masking Sohil Mehta
2025-07-09 11:00 ` Kirill A. Shutemov
2025-07-11 0:42 ` Sohil Mehta
[not found] ` <20250707080317.3791624-5-kirill.shutemov@linux.intel.com>
2025-07-09 1:19 ` [PATCHv9 04/16] x86/cpu: Defer CR pinning setup until core initcall Sohil Mehta
2025-07-09 9:38 ` Kirill A. Shutemov
2025-07-09 17:00 ` Dave Hansen
2025-07-31 23:45 ` Sohil Mehta
2025-08-01 0:01 ` Dave Hansen
2025-08-01 4:43 ` Sohil Mehta
2025-08-01 14:22 ` Dave Hansen
2025-08-02 18:51 ` Kees Cook
2025-08-04 6:55 ` H. Peter Anvin
[not found] ` <20250707080317.3791624-14-kirill.shutemov@linux.intel.com>
2025-07-09 5:12 ` [PATCHv9 13/16] x86/traps: Handle LASS thrown #SS Sohil Mehta
2025-07-09 10:38 ` Kirill A. Shutemov
2025-07-11 1:22 ` Sohil Mehta
2025-07-11 1:23 ` Sohil Mehta
[not found] ` <20250707080317.3791624-3-kirill.shutemov@linux.intel.com>
2025-07-09 1:08 ` [PATCHv9 02/16] x86/alternatives: Disable LASS when patching kernel alternatives Sohil Mehta
2025-07-09 9:35 ` Kirill A. Shutemov
2025-07-09 16:58 ` Dave Hansen
2025-07-25 2:35 ` Sohil Mehta
2025-07-28 19:11 ` David Laight
2025-07-28 19:28 ` H. Peter Anvin [this message]
2025-07-28 19:38 ` David Laight
2025-08-01 0:15 ` Sohil Mehta
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