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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-429952d5773sm36299466f8f.27.2025.10.30.14.13.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Oct 2025 14:13:20 -0700 (PDT) Date: Thu, 30 Oct 2025 21:13:18 +0000 From: David Laight To: Sohil Mehta Cc: Andy Lutomirski , "H. Peter Anvin" , "the arch/x86 maintainers" , Dave Hansen , Thomas Gleixner , "Ingo Molnar" , Borislav Petkov , Jonathan Corbet , Josh Poimboeuf , "Peter Zijlstra (Intel)" , Ard Biesheuvel , "Kirill A . Shutemov" , Xin Li , David Woodhouse , Sean Christopherson , Rick P Edgecombe , "Vegard Nossum" , Andrew Cooper , Randy Dunlap , Geert Uytterhoeven , Kees Cook , Tony Luck , Alexander Shishkin , , "Linux Kernel Mailing List" , Subject: Re: [PATCH v11 9/9] x86/cpu: Enable LASS by default during CPU initialization Message-ID: <20251030211318.74d90c3f@pumpkin> In-Reply-To: References: <20251029210310.1155449-1-sohil.mehta@intel.com> <20251029210310.1155449-10-sohil.mehta@intel.com> <789ADBB5-F7AC-4B08-B343-F23260FB8FBC@zytor.com> <13681100-ddc3-4ef0-bd13-744282324ff1@app.fastmail.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Thu, 30 Oct 2025 09:44:02 -0700 Sohil Mehta wrote: > On 10/30/2025 8:45 AM, Andy Lutomirski wrote: > > On Thu, Oct 30, 2025, at 1:40 AM, H. Peter Anvin wrote: =20 > >> Legacy vsyscalls have been obsolete for how long now? =20 > >=20 > > A looooong time. > >=20 > > I would suggest defaulting LASS to on and *maybe* decoding just enough = to log, once per boot, that a legacy vsyscall may have been attempted. It= =E2=80=99s too bad that #GP doesn=E2=80=99t report the faulting address. > > =20 >=20 > Unfortunately, CONFIG_X86_VSYSCALL_EMULATION defaults to y. Also, the > default Vsyscall mode is XONLY. So even if vsyscalls are deprecated, > there is a non-zero possibility someone would complain about it. Presumably a command line parameter could be used to disable LASS in order to enable vsyscall emulation? That might let LASS be enabled by default. David